I found this (your) post whilst searching for a solution to the same
limitation in Windows XP, & therefore whole heartedly agree with your
suggestion.
Similarly, I use a high speed 3.5G mobile [HSDPA(high speed data packet
access)] connection over a Nokia mobile, linked to my PC via USB, and found
the same problem.
Depending on OS and/or mobile phone driver version, it seems that the
maximum port speed (baud rate) can vary, at intervals, from 115200 (or
possibly lower) to 460800 or 921600, but no higher... [found through modem
options in control panel]
Interetingly though, it doesn't necessarily seem to actually limit the data
transfer rate whilst the connection is in use, at least in my case, as it
would often test far higher (using various reliable broadband speed testing
websites) if any higher speed is available on the mobile network at that time!
[Connection speeds over mobile networks are dependent on many more 'real
world' factors and is beyond the scope of this reply, but worth
investigating...]
Perhaps the 'real' (actual) data rate you can obtain is mainly determined by
the transmitters, receivers (nodes) and servers of such a network?
For example, the 3 Mobile Network is theoretically capable of a maximum
connection of 2.5-3Mbps (under the most ideal conditions, when extremely
quiet), and it is only possible to get close to these speeds at certain
(unsociable) times of day..!
Far more importantly, it appears [after much research] that configuring
protocol & packet settings are far more important to maintain an efficient,
and thus higher speed connection.
Plenty of information can be found on the web as to the best ways to 'tweak'
these settings manually for increased speed without adversely affecting
transfer integrity, or a small number of free or trial connection
configuration software utilities/tools can be downloaded here & there to do
just this.
[One I would recommend is 'TZ Connection Booster' as it sets all these
variables according to the type of connection you specify, whilst also
explaining & guiding you through during setup...]
Furthermore, one always has the option of using a connection 'booster' that
simply limits the amount & type of information downloaded during the page
loading process, or even a simple ad-blocker, etc, etc...but I digress.
So back to the original point, if it indeed matters now; surely it would be
a simple thing for someone kind enough at Microsoft to take the time to patch
their generic drivers or code in a simple registry edit for all of us Vista &
XP users in need out here, in a world of rapidly increasing mobile data
network capabilities, so that we can at least have the option of
setting/choosing our maximum modem port speed in line with the speeds that
are currently available.!?
Hopefully 'they're' not going to say 'it's not our problem', that it is up
to each individual mobile phone network or manufacturer to all improve their
drivers, as they're all probably (with luck) making use of Microsofts own
generic modem drivers..?
Fixing this one small thing, with such a large scope, may even improve
customer satisfaction a little...
We live in hope!