I have to agree. It’s all well and good to have the top x apps of right now, but the next big app will be written for iOS first. That’s a big reason to think carefully about a WP (or Android for that matter) buy.
I found that I started using my iPhone for a much narrower range of tasks once I got an iPad. Theoretically this would make switching to a different phone OS much easier because I don’t rely on a lot of niche apps. If this phenomenon is or becomes common (and people don’t mind stepping outside the halo effect of their preferred brand) it could open the doors for more users of WP, FireFox OS etc.