Device Form Factors

When it comes to mobiles there is a wide variety of device form factors to choose from and cater for. What I don't understand is why some manufacturers choose to segment their devices for business and entertainment use. I for one want to use my mobile to send email, manage my calendar and watch movies and listen to podcasts. Blackberry and Palm are definitely focusing on the business market - why else would you need that keyboard. The Palm Treo also has a square screen which isn't best suited to watching wide screen content.

In my opinion, the Apple iPhone and HTC Touch Diamond strike a better balance. They sacrifice the keyboard in favour of more screen realestate.

Now the HTC G1 running Google's Android tries to have the best of both worlds with its slide-out keyboard and iPhone sized screen. My question is, is the addition of the keyboard really worth it, given it is nearly 20% heavier than the iPhone?