What browsers does Angular work with?
We run our extensive test suite against the following browsers: Safari, Chrome, Firefox, Opera, IE8, IE9 and mobile browsers (Android, Chrome Mobile, iOS Safari). Angular FAQ
An explanation for the decision to cease support for IE7 can be found in this presentation (starting at 36:18 in the video):
Q. Which browsers do you support?
A. "…IE starting from version 8. You could do 7 but we just gave up on 7….not because its impossible… it is just so painful to debug… we just said this is a waste of time, lets just focus on IE8." Igor Minar
Seeing that IE7 has less than 2% of the browser market it probably is a waste of time for the Angular team to dedicate resources to this work.