It was just a rumor I'd read, and it would be ideal for me, but I tend to agree with you. Maybe not so much that they want to keep that sensor exclusive in the D300, but if a D90 or whatever had the D300's sensor, I'm guessing there might not be enough difference in the price of the two bodies to justify both of them. Or if there were a significant price difference, it would cannibalize the D300's sales. The whole thing seems a little weird though. The D80 is the camera that is ripe for updating, and this purported D60 looks like nothing more than a D40x with some dust reduction features thrown in. That's pretty anti-climactic, IMO. Why even bother?
It does look like the least significant entry-level upgrade of recent times... the new Canon XSi picks up a few features from the 40D and gets a brand-new sensor, the new Pentax K200D gets K10D bits like weathersealing and Sensitivity Priority mode and adds dynamic range controls, the Sony A200 got some decent upgrades over the A100, and I don't remember what all the Olympus got but it got some big upgrades too.

It doesn't really help that the D40x exists at all! That makes the D60 seem like even less of an upgrade. I'm sure the D60 will still be a great camera but not a compelling upgrade for existing owners.
That's probably true, but I wish they could. I have small hands, and it would be great to have the functions and IQ of the D300 in a body the size of the D40. The D80 is quite a bit larger than the D40, but still not as ginormous as the D300.
Actually, I was wrong about sensor size, I got mixed up and was thinking that the D300 had the 1.3 crop sensor, when it has the usual-size 1.5 crop sensor. So it should be able to fit into smaller bodies - but again, I think they'll want to keep that exclusive and that means lower IQ for the entry-level. Similarly, I'm sure that the Canon XSi's 12mp sensor will not have the IQ of the 40D, just like the XTi's 10mp doesn't have the IQ of the 8mp 30D.
That's the thing that has me toying with the idea of switching to Pentax. If the K20D is all it's cracked up to be, it could be tempting. When is it due to be available?
Supposedly mid-March to early April. I actually pre-ordered mine this morning through
Amazon 
though I will cancel and order elsewhere if I can find a better deal or some way to get it sooner. If it's not available by near the end of April (when I head for Florida), I'll probably cancel the order and buy it later in the year when I can save a couple hundred or so. Everything I've read about the K20D so far has said that the image quality is absolutely astonishing, very competitive with the Canon Mark 3 and Nikon D3. The sample shots have all been very impressive. (There's some
here taken with beta firmware, the shipping firmware should be even better!) However, the K20D certainly doesn't have the outrageous continuous shooting speed or ultra-exotic autofocus systems of those cameras, but then, it costs about a third of the price.

(And it does have stuff like the intervalometer, better than the D3's and which the Mk3 lacks, and genuinely useful stuff like TAv mode, Sv mode, Hyperprogram, etc.) It's also been compared to those for HDR, as it has the dynamic range and exposure bracketing controls to join those as the best 3 cameras for HDR.
But that's off-topic, this is a D60 thread so I'll shut up, I've said too much off-topic already.
I'm sure we can all agree that hopefully the D90 will be a bigger step forward!