rocknbil - 3:21 pm on Mar 12, 2012 (gmt 0)
Everything has to rasterize (bitmap) to 72 DPI for browser rendering anyway (unless you plan in using some vector rendering which requires a plug in.)
Illustrator creates vectored art, Photoshop, rasterized. The advantage to using Illustrator is that it's device-independent, that is, the vectors are rasterized on the device at whatever resolution they are needed. A good application would be if you plan on deploying art in multiple mediums. You can use one logo are for print medium (300 DPI) and web (72 DPI.) If you were to do the same in Photoshop, you'd have to create the logo at the largest size you'll need it, then reduce from there - and even then, interpolation can cause differences in rendering quality one way or the other. It all depends on what you're trying to do (i.e., use the right tool for the job.)
If you're just developing for the web, a program that works with rasterized bitmaps is all you need - Photoshop, Gimp, etc. There is a slight advantage to using Illustrator in that some effects aren't available in raster programs, but they can be emulated.
I've coded a few sites that were "designed" in Illustrator only. It seemed like a lot more work to extract the files needed for the site.