Depends on the devices you want to support, my E900 shows normal sites rather well, and allows me to interact with touch screen rather well, but then my E71 would definetely work better with mobile site desings.

The difference is that mobile web browser capabilities on handling different CSS, HTML & JS functionality is generally more limited than with PC browsers, also internet speed is generally slower, as well as available memory. And UI's are smaller, as well as you can not expect people to have a mouse with all buttons.. etc.