And on top of that, Ullrich was a monster. Working on the front didn't hurt his chances because he was the biggest talent of the era, but that doesn't mean it was a good idea.
Henao isn't a realistic contender for the podium? Maybe. Personally I don't think he will podium, but that doesn't mean he absolutely couldn't. The thing is that it's disrespectful. You sign a rider to see how far he can go in Europe, you take him to the Giro to see if he can win the white jersey or whatever (which probably entails at least a top 10), and then say "screw that, let's make him work for no gain whatsoever". Another Cav win is very important for Sky, of course, especially publicity-wise, but as I said it wasn't even a matter of "make Henao work, or there won't be a sprint".
I'm all for having new talents earn their spot and work their way up the team hierarchy, but in order to not be a moronic use of resources that would entail working for Urán, not for Cav. That would be respectful to the rider and his abilities.
Besides, in the long term, it's not very wise. The message they're sending is that they care more for Cav winning a stage than for anything else. It's a bit like the whole "winning the Tour with a Brit" thing. Good luck attracting foreign talent if you take that too far.