A flie system-based solution is good. You just have to take care that there wouldn't be very much files in the same directory, in which case the search would get slow. (You don't have to worry about that if you use a new filesystem like reiserfs, but that has disadvantages too.) The operating system will also cache some of the disk data to the memory, but that's for only a short time.

A database has more advantages if the records (in this case the web pages) are smaller (it costs less disk space); or if you have to make more complicated operations with them than just finding one given the name, which you can not do with a filesystem.