In fact, I suspect most want to develop for two. Having all your apps on just one platform is putting all your eggs in one basket. As Amazon found with Apple, a platform can pull the rug out from under a developer pretty quick by suddenly demanding, as Apple did, a 30% cut of the action that they had not previously. Amazon recovered nicely with their HTML5 app that bypasses Apple's AppStore. The mere existence of Android as competition should keep some of Apple's avarice at bay, at least to some degree.
Back to the Touchpad. A third platform needs apps, and thus developers to make them. Getting the hardware out there was part of the battle, Courting the developers takes time. Which is why HP's impatience with the platform seemed odd.
Today, Daring Fireball has a possible explanation that makes so much sense, I suspect it is right.
In a nutshell, Palm was purchased by the previous CEO. The new CEO is the former CEO of SAP. He does not know, nor care about, the PC or Tablet world. He is an Enterprise guy. His acquisition is Autonomy, an SAP like company.
So he has been planning to transform HP into an SAP like company. The hardware business has to go.
Might have been nice to pickup an Touchpad for $99. Or five. As my brother said early in the life of the iPad, he wants them cheap enough to have in every room of the house. But on the other hand, with Android tablets coming in now under $400, having an unsupported tablet makes little sense. Maybe hackers will get Android running on it, but how well? I had a period in my life when I tried to get also rans to behave like the big guys. I actually owned a PCJr. at one time, and had a floppy drive for my Radio Shack Model 100. Never as satisfying as a "real" solution.