As the Microsoft MVP noted, purchasing additional licenses from MS can
save you little money over full o/s. But, there are options that may
make it more palatable.
Let's say you are using Ultimate - which is awesome (as long as you
have the PC power for it). Full retail O/S is $389.99.
Upgrade is $259.99
But since Tiger offers a version intended for the system builder,
called the DSP, you can get it for $199.99.
Tiger is not the only place you can get an OEM (or DSP) version. They
are widely available from many sellers.
However, anybody buying one of these should be aware that it comes
with the following disadvantages as compared to a retail version:
1. Its license ties it permanently to the first computer it's
installed on. It can never legally be moved to another computer, sold,
or given away (except along with the original computer. If the
computer dies, the license to use Windows dies with it.
2. It can only do a clean installation, not an upgrade.
3. Microsoft provides no support for OEM versions. You can't call them
with a problem, but instead have to get any needed support from your
OEM; that support may range anywhere between good and non-existent. Or
you can get support elsewhere, such as in these newsgroups.
That first disadvantage is the most serious one. It can make it a very
poor deal for many people.