Having recently picked up a 2001 Prizm LSi, I can answer my own question (if anyone cares): yes, the Prizm's front door speakers were riveted in too (the rear speakers, OTOH, are screwed into the shelf). And this is at least partially the fault of Toyota, because supposedly the newer Celicas use riv...

Not to tire out a 5-year-old post, but CocoCarl does indeed kick (removed), and is a lifesaver besides. Thanks to those pictures on page 1, I now have infinitely better 6.5-inch Infinity Reference 6012i's standing in all four doors. The operation took more hours than I'd care to admit though, thanks...