MSAS is Beta 1 and Windows Defender is the next generation of the same
product and thus the Beta 2 tag.
AFAIK Microsoft has not stated how long MSAS will be updated, but I expect
until it expires in a few months.
There are other options for those unwilling to install SP-2 such as AdAware
and SpyBot S&D.
It is not so much Microsoft forgets those without SP-2, it is more Microsoft
is encouraging those without SP-2 to increase the security in their
computers.
SP-2 really has nothing to do with the speed of the computer so your
reference to "blinding speed" is confusing.
If your computer is fast enough for Windows XP, that is enough for SP-2.
The Service Pack Installation Checklist can help prevent installation
problems with SP-2:
http://www3.telus.net/dandemar/spackins.htm