this is a good point, however, when you view the boards, you only get 20-30 (or whatever the number is) threads per page. Searching is much faster than having all the posts in one forum "room". Even if you merged the 4 main PHP divisions into one, people would still continue asking the same questions.
One of the things we've done to solve (or atleast help) the problem is create stickies in the Newbies, General Help, Database, and Coding forums. These are frequently asked questions or common problems that are addressed.
Also, the Resolved feature was added to help people searching find their answers quicker. Unfortunately, a lot of people still aren't using it; but it is getting used a decent amount. Also the mods are going around and marking threads resolved that have already been answered.
Cgraz