I don't believe it supports Mac. You are correct... the desktop software is not necessary.
Honestly, I rarely use the desktop software. When I do, it is simply to review transactions while my Blackberry is charging. I enter all my expenses via my Blackberry usually as soon as the transaction is made. I compare my withdrawals/deposits about once a week with my online banking to ensure I'm good to go.
You can download a trial version here: Handango
OTA download: Ascendo Money
Also, I just noticed in the latest version of Blackberry Connection that Ascendo Money was one of the featured software products and they are offering a 20% discount through April 30. More info about 20% discount here: Blackberry Connection