The answer to the original question is simple: competition!
Only the top-top-top-of-the-line "big name" cards are faster than the cheap ones. Most cheap "hi speed" cards are a bit faster than the expensive SanDisk Ultra 2 - but the SanDisk Ultra 3 writes faster than almost any others, but for a
big cost!
A couple months ago, I did a list of all the SD cards I could find info on and their read/write speeds. Read speeds are what are usually advertised (ie, 60x, 133x, 150x, etc), the write speeds are what vary a lot. But still, a lesser-known 133x-150x will generally be as fast or faster than anything else, excluding the hi-buck Ultra 3 and one or two others (I think there was a Kingston or maybe Lexar, and maybe a Polaroid, which was one of the others rebadged, I think.)
Of course, most cameras aren't nearly fast enough to hit these high speeds so it's often a waste to spend the big bucks.
Myself, I'm too cheap to pay for a SanDisk SD card (I do have a couple SanDisk 2G MS cards since there's not much choice!), I have an Ultra 133x and a PQI 150x and they're fine, though the first PQI was DOA, so I UPSed it back PDQ and everything is AOK with the replacement. YMMV, though.
I keep an eye on the buy.com emails and they often have outrageous deals on SD cards, as do a few others places.