The reasoning is that the iPhone experience would suffer since background applications would easily slow down the phone, eat trough your battery and - worst case scenario - make the entire system unstable and unreliable.
The iPhone 3.0 software is finally available and for me, one of the most important (and until now uncertain) features is the ability to tether - to use your phone as a modem for your laptop when you are out and about. Your laptop connects to your phone using Bluetooth and then your laptop is able to make use of the phones 3G or GPRS connection to connect to the Internet.
Palm Pre is finally available although only on one carrier in one country so it will not make that much of a difference. Still, it is great to see another brand new mobile operating system (Palm webOS) out there - this is putting additional pressure on Nokia and Microsoft to replace their aging operating systems Symbian and Windows Mobile.