Re: how to hide paid apps from software-center?
I don't really have a happy answer for you, but rather a few questions. I'm not trying to be rude, but it's probably going to be interpreted that way:
What's wrong with looking at the license terms and see if they're agreeable to you? You really should do that no matter if it's "free" or not.
Why is it so painful to see all available options? Does Google have an "only free" button, and do you use it anyway?
Ubuntu's mission is to make a distribution which works well with other computers in a business environment, and in order to do so some commercial options are a really good idea. This is one of the major decisions a distribution makes: Whether or not to allow non-free software to be easily installed. There are lots of distributions which decide against, Ubuntu decided for it. I use Ubuntu because it allows easy installation of non-free software.
Help stamp out MBR partitions. Use GPT instead!