From the SP2 update notes:
http://technet.microsoft.com/en-us/library/dd335036.aspx?ppud=4 wrote:
SP2 removes the limit of 10 half open outbound TCP connections. By default, SP2 has no limit on the number of half open outbound TCP connections.
They originally did this to try and slow the spreading of viruses, malware, etc... but the side effect was that it made our applications and scripts that use a lot of connections (like bittorent) suffer. On XP there were third party patches that raised the limit, but with Vista it was a much bigger hassle because the OS would have problems booting if it detected changes with the file because of digital signatures.
Overall, I'm glad they decided to remove this limit.