I hear people all the time insult the way Mojang updates, "What's this pre-release crap?!" "Even though it's official they still make pre-releases?!" Yes, I'll admit it's a bit unorthodox but minecraft is an unorthodox game. And besides, the more testing that gets done the less bugs. Just because they don't use the usual method of *release* *find bugs* *squash* and instead do: *pre-release* *find bugs* *squash* *more playable release* which imho is better.
Personally I support the idea of the prereleases, but I find playing them COMPLETELY ruins the magic of playing the finished update. I ignored all posts about 1.9 and when I went into 1.0.0 I was totally blind. If I had spoiled everything by playing the prerelease, 1.0.0 would not have interested me at all.
Mojang just wants people to bug-test the next update, but they call it a pre-release.