And 90 degree stems of this type bolt in just the same. You just have to get the right brand. You want the nut on the OUTSIDE, so that air pressure holds them in. I've never had a set leak, and yes I've used them. But they didn't have them locally, so I just used the straight ones most of the time. The ones linked to above with the nut on the inside is a BAD idea. I've had the nut on the outside be a tad loose on my wifes rim once... made a tiny leak- but all you have to do it just tighten it and it's good. if it was on the inside, I'd have had to pull the tire off the rim to get in and fix it. No thanks.
The ones I got had the nut on the inside, too; and I was assuming all 90* valves are that way because how would you get the body of the valve through the hole?
I still think the BMW way is awesome.