Swiping & tapping lead to sometimes undesired results. Maybe I only want to swipe the page or tap to the sides to change the page, instead of wondering where I should tap from to make that happen. Tap invokes keyword lookup. Maybe I'd rather have it switch into keyword lookup mode for that to happen.
No page numbers relative to the printed book. Maybe this is a relic of the past, but at least Google Book Reader matches up your location with physical page number for some books.