Nikon has developed a system of in-camera chromatic aberration removal, by which the camera recognizes all the AF Nikkor lenses, and based on the known image characteristics of all the lenses, the in-camera image processing can remove vestigal chromatic aberration from the pictures: no other camera maker can do that in-camera.
It's really not much different than Canon's
Peripheral Illumination Correction. Not that it does the same exact thing, but both take care of minor fixable post production issues in-camera. One does CA the other does vignetting, and both are easily addressed in PP. Having long since ditched lower end lenses, CA is virtually a non-issue to me, but it's nice to see Nikon cater towards their low end glass with this feature.
Edit: yeah, if there are issues with CA, shooting in raw makes it even easier to deal with.
No, peripheral illumination correction is not even remotely similar to chromatic aberration correction. The two are entirely different concepts and different features. And,seriously, chromatic aberration is not a "minor" issue--it is one of the single most detrimental optical flaws that ruin images.
It is a significant issue with most of the EF-S lens lineup, especially on the newer high-density sensors like those sensors found in the T2i and the EOS 7D; it's kind of sad really, to see how even the 17-55 EF-S, a very costly lens, is not well-corrected enough to alleviate chromatic aberration at the short end when it is used on the EOS 7D and its almost 18-megapixel sensor. The low-end Canon kit lenses are significantly worse in terms of their chromatic aberration problems; Canon has hit a "wall" in terms of small pixel size and pixel density on 1.6x sized sensors; the lenses they have in their lineup were not designed with this type of pixel density in mind, and Canon will need to re-compute and re-engineer a number of their lower- to mid-priced lenses as pixel density moves to 18+ MP on 1.6x...otherwise, there will be absolutely no increase in net resolution and total optical performance for the vast majority of users using "traditional" lenses. Look at Sony's 70-200 f/2.8 lens review at dPreview: it is a 2003 Minolta designed lens, re-badged, and it get dinged for it inability to deliver high enough Modulation Transfer Function figures on APS-C; in other words, it's a film-era lens designed for full-frame,and it's NOT optically good enough on new, high-MP count APS-C sensor sized digital bodies.
There's a very real reason Canon has had to re-design its 24 and 45mm shift lenses, the 100mm macro, and the 70-200 f/2.8 L-IS,and the 16-35-Mark II /2.8 L, as well as a few other lenses: the newest sensors, with the tiny pixels packed ultra-densely, absolutely require high-resolution lenses that are almost totally free of optical problems. Stuffing 18 megapixels into consumer bodies does not automatically lead to higher resolution or better picture quality, especially when the lenses most buyers will use are older designs that were engineered either for film use, like the now ancient 28-135 IS (1992 design, sold as a kit lens with the 7D in the USA, but NOT Japan or Europe), or the cheap kit zooms designed originally for 8 or 8.2MP sensors.
All the camera makers are either at, or approaching this "wall" of lens ability vs sensor resolution demands.
In the "consumer" category, where the EOS 550D and the Nikon D90 both reside, the typical user is a JPEG shooter and a user of flash for many indoor/social photography situations, so that's one reason the in-camera CA correction is a feature Nikon has gone with in the D90, and it's also why the Canon T2i has so many Scene Modes on the top dial--both those cameras are aimed at casual "consumer" users who just want good pictures with affordable bodies, as well as video clips. Canon's video sizes are hugely bloated, but higher quality than the Nikon offers. But then, quality usually has costs or penalties associated with it. I think the Original Poster's premise is typical of the degree of confusion and surprise many consumers and beginners are confronted with when they find out that a 12.2 megapixel camera produces pictures that are as good as, or better than, a competing company's 18 megapixel camera--they can hardly get past the megapixel hype,and are surprised that more is not always hugely "better".