As extra sidenote:

as it stands now, there seems to be no way to differentiate between different CentOS major versions.

all the known facts, regarding OS versions

lsbmajdistrelease 6
operatingsystemmajrelease 6
operatingsystemrelease 6.4
lsbdistrelease 6.4
operatingsystem CentOS
lsbdistid CentOS
lsbdistdescription CentOS release 6.4 (Final) <--- Using regexes we could match this one as "^CentOS release 6\."
lsbdistcodename Final <--- this one being the major culprit, All CentOS releases are codenamed Final
osfamily RedHat

We actually fixed this use case with a custom fact as follows:

Facter.add("familygeneration") do
setcode do
family = Facter.value('osfamily')
major = Facter.value('operatingsystemmajrelease')
major = Facter.value('lsbmajdistrelease') if major.nil?
family + " " + major
end
end

Probably there are still some use cases in which regex support is more neat.

Greetings Finke