I find this very interesting. Why would Horner and Whitmarsh be against in-season testing? What do they gain from it? I think we all know...Don't we? It's all about Ferrari, a team which was famous for its ability to improve dramatically during the course of the season when in-season testing was available - something to do with a private test track at Maranello...
RBR and McLaren are obviously of the opinion that their Wind Tunnel data is superior to their nearest rivals (which is true in Ferrari's case).
Whitmarsh was very philanthropic about the whole thing claiming:
"We must also safeguard the interest of the smaller teams, who do not have great financial means."
(obviously McLaren care a lot about the smaller teams!)
While Horner simply stated: "We are not interested in the idea of allowing private testing during the season". He did say that it would inevitably lead to rising costs but not in the patronising, philanthropic tones of Whitmarshes quote.
It doesn't really increase Ferrari's costs as all they have to do is open the garage doors to go testing and the only cost arising to RBR is the cost of transport to Austria to Dietrich's new, privately owned, and redeveloped F1 track, the old A1 Ring. I'm sure there may even be a RBR factory constructed there in the near future.
Luca (see the way I'm addressing you in every post now) maybe you should look at poaching some computer and wind tunnel boffins from RBR and McLaren for 2012. Particularly since Ferrari will be in the sport for the foreseeable future - though I note you didn't get your way with DRS.