Fragmentation. The myth that just refuses to die.
AFAIK, the only apps that don't work with certain devices are Tegra Zone apps, because they've been filtered out of any non-Tegra device. And in cases, notably for EA games, where they've only 'approved' a specific set of devices. Anything not on their list will still showing Play Store, download, and install, but you'll get a nice little error informing you that your paid app isn't compatible with your device. Not the fault of Android, rather, EA's shitty business ethics. Outside of those, I've found no apps that have issues on the Tab 8.9.
I'll grant this. I do have to reboot my Tab 8.9 every other week or so. Samsung's TouchWiz UX isn't good. But its far from even a mild annoyance.
If the OP and his wife want a smaller device, or already have vested into the Android platform, or don't want to fork over 100+ more for an iPad, than the Tab 2 is a great choice.