Calc was chosen because complete sources were available, it’s a fairly nice app, and the license wasn’t GPL. Anyway, it is going to receive some GUI updates and some new features as I find time to work on it. Of course, if someone else would like to work on it, I would welcome takers on the choice. 
Sorry, I’m a bit confused. In the Open BeOS mailing list, people are talking about DeskCalc being the Chosen One. Exactly which app is it that has been added?
Calc, written by Peter Wagner, has been added to the tree. This is not to say that it will stay that way. The sources of DeskCalc have been obtained (which I was not able to originally do), along with files to fill in the missing bits in the source package. AFAIK, Stephan is going to remove what’s there and check DeskCalc into the tree after working on it as described on the list. While I am currently using Calc (the one in the tree) as my main calculator on my machine, I have tried DeskCalc, I like it quite a lot, and I intend to install a copy of it when I get a chance. It’s a nice app.