Can Apple block someone for updating?
The Problem is, he is using 10.9.4 - which is the newst OS Release.


Public BETA Release was the same as the Final one
He has a newer Seed Number or Same Build Number so he don't have to update


he can try the Combo Update but on his own riskt. Make a Backup bevore.

And in the Other Answers are some huge misunderstandings:


OS X 10.9 is and will be FREE FOR ALL
Apple Changed nothing for 10.9 user to Yosemite Servers 
there are now Public Betas for everybody
Apple is still seeding beta updates for Mavericks