It would seem that the conference call originator needs the greater capacity CPU and that this capacity may always set some sort of limits. Skype call quality is better than any telephone service and Skype certainly is my first telephone of choice. There are a lot of lower quality consumer levels CPUs, so it seems sensible that Skype should set some basic off the shelf software limit when you first start using their software. However there should be a Skype Conference Call group testing service similar to the call testing service currently provided. Calling the Skype Conference Call test bot could allow a connection speed and CPU speed test advising what Advanced Skype Conference Call settings your PC may be set at. Dual core; yawn, when will we have Quad core? Perhaps in the mean time someone will write an application that allows chaining together several conference call groups together?

Perhaps Maxxuss has a solution for AMD users?
Unleashing 10-User Conferencing in Skype 2.0 for Windows.

AMD vs. Intel Lawsuit: Subpoena for Skype
SkypeJournal Technical Editor Bill Campbell said last month that if he really couldn’t do Skype conference calls with more than 5 people just because he has a non-Intel PC he was going to “start a revolution.”

When Intel Calls, Skype Listens
The latest version of Skype’s Internet-calling software can host up to 10 users on a conference call, but only if your PC has a dual-core processor from Intel, Skype and Intel announced.