Google has never really pushed Android tablet apps in a very pro-active way. When they announced Honeycomb, they basically told developers and everyone else that apps will just "scale". While that was technically correct, from a user experience point of view, it was a terrible thing to say.
That mistake ended up slowing down the growth of Android tablets for at least a year and a half, until they launched the Nexus 7, and developers finally started to think that maybe they need to optimize their apps for tablets, too. In the end, that helped other Android tablets become more popular, too, but I think Android tablet apps are still nowhere near as many as iPad apps (hundreds of thousands), which is why Google needs to give a lot more incentives to developers to make them.
A new announcement from Google says that they may just do that soon, with a new change to the Play Store, that will show tablet users only tablet optimized apps by default. The user will still be able to change to all the apps (including phone apps), if he wants a certain app that doesn't appear in the "design for tablets" category, but this move seems like great encouragement for developers to start cranking up their tablet optimized apps.
I do hope that Google is taking this move seriously, though, and doesn't show apps that are actually still phone apps, like they've done so far, by showing apps such as Twitter or Facebook in the tablet category, even though they had no tablet optimized app before. If they do that, then this whole change would be pointless.
I do think this time they'll do the right thing, because if they plan to make Android 5.0 more optimized for notebook-style machines, that means Android apps need to look good in landscape mode and on screens that are even bigger than 10" (think 11.6"-13"). Right now most Android apps would look awful on such screens, and I think Google is well aware of that.
Android 5.0 is most likely coming out next year sometime between next Google I/O and November 2014, so if they force developers to make apps optimized for bigger screens now (starting with November 21), that gives them about a year to showcase Androidbooks that "have apps", and can actually be useful as Windows machine alternatives.