Depends on your other data in the database too though... just the fact that you only have 70 pages doesn't necessarily mean it has to be small... what sort of data is being stored on those pages? Do you have any document management modules that store documents (or images) in the database instead of the filesystem?
Our intranet has over 1000 pages, 800 users, ~80 security roles, etc, and we're barely pushing 80mb in the database... I keep my sitelog and eventlog cleared out (at least once a week) and don't store any "extraneous" data in the database -- we have that all stored on a fileserver that gets backed up nightly in it's own job.
I agree that they database may have something whacked with it and needs to be ran through some utilities to crunch it, but be sure to do some integrity checks and whatnot before that. can't remember the exact command... DBCC i think is the base command, but then there are tons of options that can run with it.
Additionally, is that the backup file including the log (ldf) file, or are you looking at just the mdf file? The log can possibly be large and needs to be truncated, just another thing to look into. I just had a database with a 25gb log file (oops.... I forgot to set up a maintenance plan on it) and had to truncate that one. Wasn't DNN related though. :)