It's a shame they didn't add it since when shooting video it's the quickest way to make sure you have critical focus if you lack a HD monitor on your rig.
Huh? Not sure I'm following this.
They did (of course) still add the ability to look at 10x magnification in live view to check focus. You just can't record at that magnification. The T2i/T3i have the ability to record a low resolution video using only the center portion of the sensor, which is what the OP is referring to. Some HD purists call it "gimmicky" primarily because it only records in standard definition, not 1080 or 720, so they find it to be useless for their highbrow purposes. I've played with it on my T2i, it's pretty impressive - I could see inside the eyes of a spider whose body was about as big as a grain of rice
I was surprised to see that my 5d3 didn't have that feature - although I probably wouldn't ever attempt to use it in a professional shoot due to the poor resolution, it would still be fun to play with. Which may be why Canon decided to leave it out - just one more "silly feature" for the stills-only crowd to gripe about having to pay for
Are you talking about switching recording modes just to check focus?