Mark, I still have to respectfully disagree. I see your points but I just can't agree with your conclusion.
1) I don't think there's any danger of Pentax disappearing any time soon. They've been around for decades and their current DSLRs and lenses are highly regarded and selling like mad. They are a smaller company and are not attempting to match the volumes that C/N move. They're making a lot of money off their DSLRs, plus they have investments from Samsung (which is not exactly a small company) and Hoya.
It doesn't take a large share of a market in order to remain healthy. Hey, look at how few cameras Hasselblad sells, too!
2) Their lineup is smaller than C/N but it is hardly minimalistic, there are many lenses available for different needs and often with superior optical quality to the competition. Again, it's going to be a rare user that cannot find a lens to meet their needs.
3) A valid point but I think a minor one.
4) I don't think that differences are that significant, especially between the Nikons and the Pentaxes. It wasn't that long ago that the Pentax K1000 was the standard photography class camera, either. That's partly why I bought mine...
5) Your main point here seems to be financial. Like I said, I could switch systems at this point with no financial hit whatsoever. This one is definitely a red herring. Furthermore, like I said, it doesn't take a C/N to do professional photography.
I see your Amiga comparison. I was always an Atari guy, starting with the Atari 400, with 8K of memory. (Ours was quickly upgraded to a whopping 32k!) I eventually went with an Atari ST due to my loyalty, even though the Amiga was slightly more "sexy" and was designed by Jay Miner, the guy behind the Atari 8bits. I didn't go into the PC world until I bought a Pentium 90. Did I feel abandoned by Atari? Not really. No I regret my choice? Absolutely not! The PCs of that era were junk as far as I was concerned, only good for stuff like spreadsheets or other basic text-only things. Furthermore, the basic knowledge transfers easily and I soon after went into the IT business as a career.
So, I have two big points.
1) Avoiding smaller companies just because they're small is, in general, not a good idea. Otherwise we're left with only large monoliths, unresponsive to customer demands. (Even the most ardent C/N fans have to admit that they haven't really been doing much interesting with their cameras lately, especially the entry-level ones.) And, it's a self-fulfilling prophecy. If nobody buys because they're smaller, then of course they won't survive. At this point, I think the only reason more people don't buy Pentax is that they just don't know that they're offering DSLRs since they don't appear in the weekly
Best Buy ads. (That's how I was until I got ready to start getting serious about a DSLR.) Once people find out about it, it's an extremely strong contender and as we can see from recent postings here, it is often the pick of an educated new buyer.
Their success of late has had a big impact on the value of Pentax equipment on eBay and will no doubt lead to more 3rd party equipment becoming available, plus Pentax isn't sitting still and has a good number of new lenses on their roadmap.
2) I think the biggest advantage, and what's been driving their success, has been just plain "bang for your buck" - and not just with a $1,000 system, but a $2k, $3k, or more system. Someone who buys a K100D and $1,000-$1,500 worth of lenses will have a more equipment than an XTi buyer who spends the same total money, and furthermore, most (all?) of those lenses will be higher quality and all will be image stabilized, unless the XTi buyer blows their lens budget on a single IS "L" lens. Another $400 gets you a K10D which offers features designed for pros to make photography easier (hyperprogram, the unique ISO modes, water/dust resistant, etc)...
Heck, with the rebates, you can get the K100D and the 50-200mm for, I think, under $700 now (off the top of my head, not running the numbers.) That's an
image stabilized 50-200mm. And an IS 18-55mm. What would a Canon owner have to spend to get an equivalent IS lens? In other words - an investment in Pentax gives you more gear with more features for less money NOW. An investment in Canon means less gear, less features, for a promise of buying high-end equipment in the future. Financially, it seems like a poor choice, as you'd have to replace all your entry-level equipment to go "pro" with Canon anyway.
While we're on the topic, I'll come from the other side. Yes, I don't like Canon very much. Why? Because I feel that they deliberately design their equipment to make you want to upgrade. Their entry-level stuff seems to be build relatively cheaply. Their cheapest DSLRs generally get poor marks for build quality and feel. Their users seem to know and accept that the entry-level lenses will feel a bit cheap and will have subpar image quality. ("Well, I didn't expect much, it's no 'L' lens!") They deliberately leave features off their entry-level cameras. (Like, why no spot metering?) I know there are firmware hacks to re-enable stuff in the original digital Rebel that was there was just disabled in software, in order to "strip down" the camera, I'm not sure if the same is true with the XT/XTi.
These issues do not seem to be as prevalent in the Nikon world. That's why, if I were choosing just one, I'd have to go with Nikon.
Of course, the reality is, we're still picking nits here. The DSLRs from all three companies are all great equipment and each is capable of producing similarly stellar quality. But for sheer bang for the buck, C/N are clearly behind Pentax, especially when you start talking IS lenses.