WinModems?

[Alice71460]

This is a newbie question I guess....

I know that a WinModem uses more software than hardware, and so is cheaper.
They also only run with Win95 & WIn98. 

My question is about the details: Why exactly is there only support with Win95
& Win98? What is left up to the software? Why is it so different that Linux,
WIN-NT, etc will not do it?

I guess what I want is a technical reference  put into terms I can understand.

TIA
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