If that's because Android's interface is laggy, then why do people keep buying Androids?
IMHO, iOS users spend more on apps because iTunes is better than Android's Marketplace - this may have been a deliberate decision by Google nonetheless. Did you know that I am not allowed to sell Android apps in the Marketplace because my country is still not approved for registering a Google Merchant account? That's right, it's almost 2012 and while I can sell apps on iTunes, I can't on Android's Marketplace. However I have no problem integrating AdMob in those apps. So it's like Google wants ad-supported instead of paid apps, which considering their main business model it isn't that shocking.
However, you can't say that Android and its UI is not a success.