Did Microsoft file aggressively, or defensively?
Those patents long predate SPDY, so the question of "aggressively or defensively" is moot. I think Microsoft, as a participant in the IETF standards process, is simply following it's duty in disclosing any patents they own that might have a bearing on this protocol. Given how broadly the claims are written up, it seems difficult for most application protocols to not infringe these patents.
So, to answer your questions in the title, there is some broad prior art, but the specific optimizations of SPDY could still have been patentable. By now, however, I'd guess the bar date to apply is long gone.
Are patents like 6,604,144 and 6269403 a bad example, compared with other historical multiplexing IP?
Your "historical multiplexing IP" patent has almost nothing to do with the Microsoft patents. The historical patent relates to "Inverse Multiplexing", which is achieving higher bandwidth transfers by splitting up and sending data over multiple lower-bandwidth channels in parallel. This is, of course, different from the multiplexing in SPDY and the Microsoft patents, which is combining multiple response objects into a single data connection.
So nobody uses [FAST TCP].
Well, Akamai recently bought FastSoft, the company commercializing FAST TCP, so apparently, no; one of the largest CDNs ever will probably be using it.
The moral of the story, I guess, is that with any innovation your choices are mainly:
- to make your innovation as widely available for use as possible, you'd want to release it free of IP and other encumbrances; or
- to make money off your innovation, you might want to protect it with IP rights, such as patents and copyright.
Either is a valid choice, and there certainly are lots of variations in between.