Marco Arment, the author of Instapaper, put together this fabulous graph:
Android tablets and the tablets of other manufacturers (e.g. BlackBerry Playbook) are selling at rates comprable to failed video game systems from the 80s.
In other words, you are likely not to get a single new customer by developing a tablet app for a non-iPad platform. Even if the cost to add support for the BlackBerry Playbook was ten minutes, it wouldn’t be worth it.
If you are writing tablet software for anything other than an iPad, you’re throwing money away.