The only technical argument I have constantly seen here is not misplacing passes. Again, I have never implied Keane was useless with the ball. He had enough ability to form a platform for his key attributes to actually flourish, but not much more than that, is my view. It is important to keep the ball, but being able to give it to the guy next to you isn't the epitome of being a technical genius. Liverpool and Swansea midfielders have been doing it for ages, and while nobody says they are technically poor (which I am not saying about Keane either) - nobody particularly mentions them as technically outstanding either.
To add, I don't think Fellaini is technically poor either. I think he is technically good enough, although his technical ability isn't his main strength, like with Keane, who was still a great midfielder. This was the basis of my comparison of the two, in the sense that he could still possibly become a great midfielder for us despite not being technically outstanding. Players like Essien (who was most United fans' first choice to replace Keane) was similar. Great player, decent ability, but no more than that. In a Ghana midfield, for instance, he couldn't do what Kevin-Prince can with a ball. Does that make him worse? Not necessarily. But it is what it is. Because he can control the ball and pass it is not a basis for people to go around banging on about Essien's technical ability.
An example of someone who, on the ball, performs many similar duties as Keane did would be Busquets - in terms of lots of continuity passes etc. That said, for those who actually want to, a difference in technical ability can still be assessed between the two. It's way to simplistic to simply say 'he rarely gives it away' as evidence of great footballing ability. Rio Ferdinand (who I also think is a more naturally/technically gifted player than Keane) rarely gives it away either, but that's largely because he passes it square to Vidic more often than not.