I'm not sure how it works on SkyQ, presumably the same, but to replace the logo on Sky+HD requires an entire new software update, its obviously not a priority thing otherwise it would have been changed by now I'd have thought.
Presumably Sky+HD is now effectively relegated to playing second fiddle to SkyQ, much like the older Sky boxes play second fiddle to Sky+HD in the update stakes. Any updates they get are just to keep them working when Sky change the configuration of things behind the scenes. I suppose in an ideal world they'd just want to force everybody onto SkyQ come what may which would save them the bother of supporting the legacy boxes but obviously that runs the risk of pushing the churn rate through the roof and also it'd be quite an expensive operation what with the boxes and the new LNBs needed.
They changed it on Q already so yeah probably not a high priority