the UAD maps its ram into the machines address space (obviously) and it also HAS to be located within the address space accessible to user space so that the users programs can load the plugin DSP code and data into it (And so that the cards DMA hardware can get at the pages containing the audio data now that IO-APICs have started enforcing that sort of thing).
The 3gb switches give you 3GB of VM available to windows clients and the UAD takes 1.2GB of this for mapping its on card memory, seems perfectly reasonable to me. Does windows not do PAE?
I suppose the UAD drivers could map the card outside the users address space but then every plugin would have to send all requests via the driver (requiring a context switch and possibly a TLB flush (both of which take time)), so mapping the card into the users address space makes sense.
This all goes away of course as soon as you roll with a 64 bit OS that does not have such a relatively small limit on the userspace vm size.
Actually it is Microsoft that is robbing you of VM, not UAD, not that that is much comfort.
Audiophiles use phono leads because they are unbalanced people!