- Bandwidth
The limited bandwidth that can be support by mobile devices currently is very small which causes web developers to reduce the usage of rich data. - Screens Size
The screen size of a mobile device is very limited. This also limits the viewing capacity of the user. - Less Powerful Processors
Due to the slow processing speed web developer would have to use server side scripting which will bring more load to the servers. - Cost of Wireless Connection
As wireless connection of a mobile device to the internet is still a relatively new technology the cost of using such connection is also expensive as the technology is still under heavy development
Reference:
http://www.witiger.com/ecommerce/mcommerceintro.htm