Honestly, because we're an app company rather than an e-commerce or SaaS company, a lot of the effort we put into these pages is largely for the benefit of the press (who often research apps on desktop). The vast majority of end users discover our apps through the App Stores themselves, so we put even more effort into our icon, screenshots, app preview, description, keywords etc.

As for conversion rates, sadly Apple hasn't opened up any analytics to developers for their actual App Store product pages (even though they announced they would a year ago at WWDC), so what users are doing when browsing the actual stores is largely a black box - we have no idea how many people view our app store previews or screenshots etc. or even where they came from (many deep-linking schemes we've looked at are pretty brittle or don't work at all).

Conversion rates on the website landing pages are pretty good - there's not much else to do on those pages than download the app, and chances are you came there with that goal.