Why is GVI a newer version than GigaStudio?
Decoding GigaStudio and GVI version numbers
GigaStudio and GVI (Giga Virtual Instrument) are both PC-based samplers, that play back the same sample libraries (for a more complete comparison, check out "GigaStudio vs. GVI")
As of this writing, GigaStudio v3.21 and GVI 3.54 are the latest software versions of each. GVI was released in 2006, and GigaStudio in 2004 - in this sense, GVI is "newer". However, the version numbers are not equivalent: GVI began with v3.5, when GigaStudio moved from v3.12 to v3.20.
Much of Tascam's product development is being focused on GigaStudio 4, which
will support Vista 32- and 64-bit, and GVI Mac, which will bring the GVI to the
Intel Mac platform. It is possible we will not see GigaStudio move up to 3.3. GVI
has been such a successful venture for Tascam thus far, we can expect
continued updates and bug fixes. 
Author
Gavin Whiteley, president
of Major Scale Audio, is the Music Playback Engineer for The Beatles LOVE by Cirque du Soleil, at The Mirage in Las Vegas. Working closely with Sir George, Gavin installed, programmed, and now operates a series of digital audio workstations, exclusively using the original recordings of The Beatles.