Oh, I know; finally did my first ground-up build last year. Im saying that the stem on the POS rental bike I've got (although not the worst that anybody's seen on BF, according to a thread I started last week) won't stay secure enough to keep itself pointed straight, at least not without cranking down the stem bolts hard enough to strip the threads. I figure that if it can be turned sideways, it can also be pushed upwards. The only thing truly keeping it all together is the top cap, and it's adding just enough pressure to keep the stem from getting knocked out of alignment.

Besides, on the roadie with its carbon steerer tube, I'd rather have the cap taking the brunt of the load and not clamp the stem any tighter than it needs to be.