well the 550D image quality is as good as the 7D.
a 7D will deliver you more shots per second then a 550D... sure.
but when you donÂ´t need the fast FPS then the 550D is as good as the 7D when it comes to image quality.
"As good" from a practical standpoint in a comparison based solely on the IQ of the sensor, probably. There are some slight technical differences in the performance of the sensor in the T2i vs. 60D vs. 7D - even though they use 'the same' sensor the firmware and in-camera RAW processing are slightly different, they have different anti-aliasing filters, etc. For example, in DxOMark scoring, they all have the same overall score, but the 7D has a slightly wider dynamic range and slightly better low-light ISO performance, but a slightly shallower bit depth. Again, though, these are technical differences that would be barely, if at all, detectable in an image.
However, there is more that goes into making an image than the sensor. Frame rate was already mentioned, but is not the only factor - and in many cases not the main one. If the AF system can't lock on using an outer AF point because the single-orientation sensor of the T2i is not as effective as the cross-type sensor in that position in the 60D, the image will be out of focus. If the shorter shutter lag and much better AI Servo tracking of the 7D enables a shot that the T2i or 60D would miss, that's a picture you wouldn't have if you had the Rebel or the 60D.
I'm not saying you can't take great pictures with a T2i, or a Rebel XS, or a 25-year old Pentax A3000 film camera (which, incidentally, was my first SLR), or a point-and-shoot - you certainly can. Nor am I saying that buying a 1DsIII will automatically make your pictures better (though it will certainly reduce your bank balance!). But better equipment can make a difference, and in the case of dSLRs, increasing cost generally means increasing quality.
There are many people out there who have one product and say that it's 'just as good' as a more expensive one, without ever having used the next level up (and by 'used' I don't mean held one in a store for a couple of minutes). Similarly, there are people who say a particular feature, e.g. AF microadjustment, is useless and call that Truth, when they've apparently never tried the feature themselves. (I thought heated car seats were useless, too, but now that I live in New England and have them in my car, my opinion has changed...but then again, I never went online and started a thread about how useless they were, much less making out that my opinion was anything other than just my opinion.)
One of canonman's frequently restated points is the the T2i is a great camera because it's so light. Now that he has a 60D, which he states is, "Definately heavier," he says, "It does feel a lot better to hold." I wonder how he'd feel if he held a 7D?