Have a look at http://www.dxomark.com/index.php/eng/DxOMark-Sensor/Camera-rankings
You can see the D90 is ranked 17. The T2i is rated 31. This confirms your friend comments.
While I can understand the hunger for higher megapixels. The large files creates storage and performance issues. Also there have been comments in the past about needing to pay a premium for professional lenses when Canon cameras go above 15 megapixels to avoid image issues.
Here's a comment from DPreview when Canon exceeded the lens design with the earlier 50D.... http://www.dpreview.com/reviews/canoneos50d/page31.asp
Let's have a look at the really important stuff then: Image quality. Below ISO 1600 image output is clean with well balanced contrast and colors and as you would expect from a DSLR with a 15 megapixel sensor the 50D delivers a fair amount of detail. Having said that, in terms of per-pixel sharpness the 50D cannot quite keep up with the better 10 or 12 megapixel APS-C DSLRs in the market. At higher sensitivities the smaller photosites are clearly producing more noise (as shown from our RAW comparisons) and so Canon is having to apply more noise reduction to keep to acceptable noise levels, this of course means a loss of detail from ISO 1600 upwards.
It appears that Canon has reached the limit of what is sensible, in terms of megapixels on an APS-C sensor. At a pixel density of 4.5 MP/cm² (40D: 3.1 MP/cm², 1Ds MkIII: 2.4 MP/cm²) the lens becomes the limiting factor. Even the sharpest primes at optimal apertures cannot (at least away from the center of the frame) satisfy the 15.1 megapixel sensors hunger for resolution. Considering the disadvantages that come with higher pixel densities such as diffraction issues, increased sensitivity towards camera shake, reduced dynamic range, reduced high ISO performance and the need to store, move and process larger amounts of data, one could be forgiven for coming to the conclusion that at this point the megapixel race should probably stop. One consequence of this is that the 50% increase in pixel count over the 40D results in only a marginal amount of extra detail.
We're by no means saying the 50Ds image quality is bad but it's simply not significantly better than the ten megapixel 40D. In some areas such as dynamic range and high ISO performance it's actually worse and that simply makes you wonder if the EOS 50D could have been an (even) better camera if its sensor had a slightly more moderate resolution.
If you look at Nikon's product, they don't have these high resolution lens issues.
