It's simple really: he's a better tennis player than Ferrer any way you look at it. He's 7 years younger and already had surgery and yet has far better achievements and victories and is far more capable of defeating the current top guys.
Odds are not made by MTF Ferrer fanboys but by people who need to put their money where their mouth is; no one who values their money could ever rate Ferrer anywhere near Delpo to win any Slam title - it's not like Delpo is likely to win the AO at all, but he could (slim chance of course) do it, Ferrer can't - he could play the very best tennis he's capable of and he still wouldn't have a chance.
Re: Ferrer ---Not strictly true if he had a favorable draw in 1st week then had Tipsy in the last 8 then a SF vs Berdych ( say Berdych beats Fed in Qfs) then plays final against Murray lets say who killed himself in the QFs vs whoever than kills himslef again in his semi win against Novak and hasn't got enough left for final....Ferrer would have a chance! unlikely sure? but not impossible.
Its unlikely DelPo would only have to play 1 of top 3, he will almost certainly need to play 2 of them at least. which makes his road very tough especially considering this is not 2009.