Q:

Why the $2.99 minimum price for apps

According to http://developer.ubuntu.com/publish/ Apps can only be published at a $2.99 minimum price, which seems to include the ubuntu touch apps. 
99% of the apps I have purchased on android are $0.99
If Ubuntu goes ahead with this, isn't it going to:
1) exclude a lot of developers/apps. 
2) or Force developers to push up the price, so that you end up paying 3x as much for the same product. 
3) or give the app away free but force more adds or in game/app purchases which are the bane of the app world. 

A:

From the Commercial Software FAQ:

What is the minimum price I can charge for software?
The minimum price for applications is 2.99 USD. The transaction fee we charge has to off-set the credit card charges, bank charges and fraud detection that takes place within the payment platform. By enforcing a minimum price we ensure that processing transactions doesn’t cost more than the transaction fee. We intend to lower the minimum price over time.

