Does the 48 Mbps in the 550d provide (potentially) higher quality image as the 24 Mbps of the Canon HF-S20/21?

You might find this an interesting read:
DVXuser.com - Articles (http://www.dvxuser.com/articles/article.php/20)

Thanks for sharing the info. To me these discussions are really beyond my interest as an amateur filmer. It is searching for weaknesses in the incredible technique that is being given to us in this time. How many real life viewers of a DVD or even a cinema movie will be bothered by these issues? Even if a trained eye catches the artifacts, it is more then compensated by the overall image quality.

yes, but you asked if a 550d would provide a higher quality image as a Canon HF-S20/21. Technically, no according to that article but the camera seems to have some tricks up it's sleeve to overcome most of those problems. I have also seen frame comparisons which highlighted the weak area's of the dslr's compared to "real"' videocamera's (even small hd handycam's) but if you place a dslr in the hands of a experienced videographer he/she can make dslr footage shine. But then again, a experienced videographer can make any footage coming from any camera shine. It's all in the eyes of the beholder. :)

experienced videographer can make any footage coming from any camera shine. It's all in the eyes of the beholder. :)
100% agree, but if we 're talking the same skills applied to the footage from T2i and HF S2xx
there is no second though, T2i is a winner, (imager) size does matter :)

Now, why do you think that T2i is the winner?

It might help if you clarified what exactly you need to know, your initial question was if the higher bitrate of the dslr would result in a higher quality image. I'm not a tech guy either but if you read the article I linked to you get a clear answer to your question if you just look at the resolution chart.

I did look at the article, but it says that 550d has issues as compared to real camcorders, but in spite of this Buba thinks the T2i is a winner over the HF SXX. Why?

Ok, but then you are asking for subjective opinions, not actual facts. To me dslr footage from what I see on the internet appears sharper and more vibrant and with less dof (and more light sensitive) then what a Canon HF-S20/21 can produce, but that's something you can judge yourself as well just looking at random vimeo or exposure videos that are done with both camera's. Eventually it all comes down to user preference, a dslr does serve it's purpose in certain area's but I would not sell my canon xh-a1 just to get it. As an addition to my xh-a1 yes, but for run and gun I gladly rely on my "real" videocamera and use a dslr for the fancy creative stuff.

Does the 48 Mbps in the 550d provide (potentially) higher quality image as the 24 Mbps of the Canon HF-S20/21?

No, because the CODEC that the 550D utilizes has very poor compression compared to the AVCHD compression used by the HF-S20/21 cameras. I suspect this is largely due to the amount of processing power required to properly compress the image stream from a DSLR camera.

To see this difference first hand, try loading a 550D video clip into a video editor that can natively handle the AVCHD CODEC ( Edius Neo 2.5, Vegas Pro 9, Premiere CS 4.2 ), and try saving this clip in AVCHD format using a range of bitrates. In the few tests I've done, the file size of the 550D / 7D / 5DMKII clips shrank by a factor of 3 - 4 with no real change to the image quality.