Sentencing guidelines change all the time. In recent years the process has become more open and public there's even a website here:
http://www.sentencing-guidelines.gov.uk/
Personally I think this is a good thing because it makes things much more visible, there are public consultations and it's clearer why judges set the sentences that they do.
People are even begining to understand what a tariff is.
I don't think the guidelines have changed with regards to these sort of cases recently, it's just a coincidence that we've had a few really nasty cases all come up at the same time.
There's a list of whole life tariff prisoners on wikipedia here:
http://en.wikipedia.org/wiki/Whole_life_tariff
2006 was a good/bad year (depending on how you look at it)