All Canon sensors include a form of analog noise removal on a per-pixel basis called Correlated Double Sampling, or CDS. This technology has been integrated into Canon's line of 500nm sensors for over a decade. It is effective, but not as effective as digital CDS (as demonstrated by the astounding low-ISO IQ provided by Sony Exmor sensors, which use a form of column-parallel ADC with digital NR.)
To my knowledge, no Canon sensors employ anything other than the basic analog per-pixel CDS from a hardware NR standpoint. Software NR has been employed for some time in firmware, and is only applied to in-camera jpeg output. I would not be surprised if a newer-generation Rebel had better jpeg software processing than the 7D. I would be surprised if any newer camera that used the same 18mp APS-C sensor as the 7D had better NR...especially a lower-end camera. Regarding IQ, there are some key differences between the 7D and the Rebel line that lead to the higher noise on the 7D.
The key differences are the higher readout rate, which demands higher frequency processors and ADC's. Higher frequency electronics tend to introduce more noise of their own into the signal they are processing. In addition to that, the 7D uses a dual Digic design to achieve the high readout rate, effectively providing parallel processing across two separate image processing chips with multiple ADC's each. That is the primary cause of the often pronounced vertical banding in 7D images. The two DIGIC chips don't process 100% exactly the same, resulting in slight differences to each vertical band of pixels processed. The Rebel series only uses a single DIGIC image processing chip, and as such have less pronounced vertical banding, which leads to more pleasing noise (if not necessarily less noise overall.)
Regarding whether "it matters"...possibly. The 7D has many benefits over any of the Rebel line. It has a much faster frame rate, a much better AF unit and drive system. It is a professional-grade body, which means it has weather sealing (not as good as a 1D series body, but still better than having none at all), better ergonomics, and many more features and functionality. The viewfinder is bigger and brighter, with a more advanced HUD. There are many reasons to get the 7D, even if its IQ is not quite as good as the T4i.
So...does it matter? That's up to you. Do you need a higher frame rate? You do if you shoot a lot of action...sports, wildlife, birds. Do you need a better AF system? You do if you shoot a lot of action. Do you need a brighter display? You do if you primarily use the viewfinder rather than the LCD screen to compose and shoot. If you primarily do landscapes, I'd stick with the Rebel line. The Rebel XSi is actually a great camera for no-action photography like landscapes...the only real benefit you might realize by moving up to the T4i is higher resolution and potentially better high-ISO performance (however for the most part landscape and other forms of still photography use the lowest ISO setting.)
