Ohh that sucks, sometimes Dell will discontinue a Inspiron/Latitude version of a laptop and keep it going for Vostro longer. I have seen the period go for upto a year that they continue to sell and I assume produce machines.
Also once a computer hits buisness class they continue to support it for quite some time. The D630, which is what we buy was recently replaced by the E series in January 09. We can still buy them, and they continue to release BIOS updates for us.
Since the Mini was selling faster then they could manufactor them, they may not have too many in stock. Which means the Vostro version won't last long enough for them to release another BIOS update, and/or better peripherals like a bigger battery.