Because I believe Apple would stick to the non-embedded market targeted offerings. Not some special corner case offerings. In the current mainstream offerings, quads cost more than duals. Intel is unlikely to change from that formula. Indeed, for leaked price quotes for desktops the pricing is unchanged from Sandy Bridge.
http://www.cpu-world.com/news_2011/2011121902_Prices_of_Ivy_Bridge_desktop_CPUs.html
Sure they could cripple a quad to putting it into a lower envelope to for the specialized embedded market, but I really didn't think those were relevant to what is possible as a MBP 13" part. Still don't.
So to get an price even with a dual they would suck the performance out of the offering (set the base GHz low .. e.g. , 1.2GHz so that it only Turbos up to what the current candidate versions.). Again that would loose generally loose out in a competition to be placed in a MBP 13".
Would a 1.2GHz quad be useful in a Small-Medium business targeted NAS box, a Windows Home Server, or low energy server? Sure. I imagine there will be a 35 (or lower) W Xeon E3 part also. The Core i3/i5/i7 version will get use from some embedded markets too.