Five HD today launched on both the Sky and Virgin Media platforms; unfortunately though Freesat isn’t expected to gain this channel any time soon.
Many, including Five themselves will tell you that the reason for the lack of Five HD (as well as Fiver and Five US) is because of space available on the narrow Astra2D beam required to broadcast in the clear as a UK broadcaster.
In reality, the reason is that Sky pay Five a nice sum of money to remain encrypted, ensuring they are the only satellite based platform with these channels. Until a time when Freesat has a sufficient number of viewers (so advertising revenue accounts for more), or Ofcom some how force Five into broadening their access, it looks like we’ll be without.