Google VP of Android product management Hugo Barra told the press that he's underwhelmed by the majority of Android-based tablets. Google's own Nexus 7 tablet is far ahead of many of its competitors and Barra comments on this that he really does think that the Android ecosystem hasn't yet put its best foot forward. One of the reasons for this is that a lot of Android tablet makers primarily focus on low pricing, resulting in devices with substandard hardware that do not provide an adequate user experience.
Of course, part of that comes with the territory, given that the operating system is free for any device maker to use with its hardware. That's led to sub-$100 (even sub-$50) bargain tablets from no-name vendors that can hype that they run the Jelly Bean flavor of Android, but rely on cheap processors, low-res screens, and other minimal specs to do it. One consequence is that tablet-optimized apps for Android are less prevalent than Barra (and users) would like.
Of course, there are exceptions like Samsung's Galaxy tablets and the effort Amazon has made to spruce up its Kindle Fire tablets (even if it tries to disguise their Android underpinnings). But Apple, and even Microsoft for its Windows 8 tablets, retain more quality control over the hardware that powers their operating systems, which has forced Google to lead by example (and resort to using a bully pulpit) in order to push its fellow Android partners to focus on a more polished product, rather than just a cheaper one.