The 650 sizes were originally made for wider tires than 700c. Each size was as it was so that, with different width tires, all the wheels would basically be the same height. Now, you can get fairly wide tires for 700C, but this makes the wheel quite tall which will very likely cause some toe-clip overlap, among other things. With a 650B wheel, you can have a nice, wide tire while still retaining plenty of clearance for your feet. Yes, 26" tires would do this as well, but on anything but small frames they look out of proportion. If you like narrow, hard tires then obviously 650B tires would be pointless for you. That wasn't their original purpose anyway. Personally, I find 700C tires below 32mm to be harsh and rough. In fact, often times I'm frustrated that my Univega doesn't have room for anything larger than 32mm (with fenders). The roads around here suck, and as a result, riding with rock hard 23mm tires sucks.