Very well put.Disregard the comment about professional results-in general. You can get top notch quality out of a consumer grade DSLR if you master the skills to do so. Somewhere down the line and under a microscope you might feel the professional pinch, but chances are you'd never be in a situation to tell the difference between images from the entry level cameras to full frame unless you got into the heavy professional demands.
The 550D/T2i was introduced in 2010. It's an incredible camera and will allow you to get what you put into it-if you learn it you will get amazing results. If you don't you'll get the same quality images as any good point and shoot can produce.
It is also not the most current camera in it's class for Canon. The 600D/T3i was introduced in 2011 and in 2012 The 650D/T4i. Does that matter? Not really much. There are definite improvements in technology, but overall the basic function of the camera is the same across the board. If you are using it for video the T4i has some major points in it's favor including auto focus for amateurs who need it-most pro's are manually focusing video so that wouldn't matter.
If you are using it for low light or low contrast situations the focus system is a pretty significant improvement from the T2i. There are 9 CROSS TYPE sensors in the T4i and one in the T2i. Does that make a huge difference overall? Not for general use, but for certain situations it might.
If you intend to be shooting in low light situations the T4i has quite a bit of benefits to it with a higher ISO allowance. If you will be shooting sports the T4i has a faster frame per second rate.
Overall, are those things enough to make me want the T4i? As a GENERAL shooter no. As a sports photographer yes.
If the T4i isn't in your budget? The T2i will not disappoint you in the slightest. Or the T3i which I haven't even tossed out it's info.