I must say, I find that incredibly funny considering Avast is the most widely used anti-virus solution worldwide according to recent research.

http://f.cl.ly/items/370j0M243B002y1w0C1B/AV-MarketShare.png

The exception to this is North America, where Avast is third on the list, with both Symantec and AVG above it.
As others have said, I am absolutely certain it is a marketing thing - they want to sell you their chosen partner’s anti-virus solution (It would not surprise me if that was Norton 360).

I hope you did not get ripped off, considering Geek Squad’s less than stellar reputation.