WAL is a Good Thing (tm). Seriously. People pay big bucks for WAL lenses, this comes with it. Not that you won't ever pay more for lenses anyway if you want to go wider, but still. The WAL is a lot handier than you'd think, especially underwater.
The big screen is also a Good Thing (tm). Especially underwater.
The extra megapixel is fairly meaningless. The write speeds of the two cameras are very different... I seem to recall the S80 is roughly twice as fast as the A series cameras. Use the camera compare function on dpreview and I think you'll see some more differences. You should also read the reviews at Steve's Digicams, the other really good camera review site.
The S80 does cost more. And it uses rechargeable batteries, which some people (like me) prefer, and others prefer AAs. But you'll definitely want two (one to charge, one to use) so consider that cost... vs. an unending supply of AAs. There are rechargeable AAs, true, but I think battery packs are just a heckuva lot more convenient.
The S80 is the higher end camera, once you really start looking at the differences. And it costs more. It's entirely up to you whether the extra cost is a problem for you, or if the added features make the extra cost worthwhile.