CRA asks for your husband's 2007 income, not 2008 income, so that if he is filing his 2008 return later than you, they can make a decison on your 2008 return right away. That's my surmise, anyway.
Well, that still doesn't make sense to me.

We hadn't even met until July 2007 and didn't marry until the following year, so to me, whatever he was making as a
single person shouldn't even matter. And he only came to Canada in 2009 so it should only be at that point that his income is relevant for CR purposes.
Anyway, long story short.. I sent a letter explaining everything that was asked and CR still took back my GST credit (they deducted it from my 2008 return). But after several phone calls they finally admitted that I am in fact entitled to the credit and will be returning it to me with interest in January. Let's see if that actually happens......