I can't understand what difference it would make between dig/analog servos. Both dig and analog servos use the same type/amplitude/frequency to operate them. The only thing different is that dig servos have a MPU instead of timing circuits and so dig servos update faster and can require more current (and provide more torque as well).
Here are a couple different articles on the differences:
http://www.futaba-rc.com/servos/digitalservos.pdf
http://www.fatlion.com/sailplanes/servos.html
http://www.rcuniverse.com/forum/m_62...tm.htm#6227638
That said, I think the proper statement
should be "Digital servos must be used to take full advantage of the high speed radio system". Kinda makes no sense to have a super fast radio but use slow servos.