I should imagine it's because the defence was the most important part of the team when we won the double, and because Ferguson himself has often said that everything is built from that foundation.
He probably recognised that we'd need to start replacing them a fair bit in advance, so that the next crop could be gradually assimilated into the first team line up. This is happening right now, in fact, and it's been made possible by making said youngsters integral squad players, ready to step up for key, injured starters.
He's so fecking clever, Ferguson. It's been an absolute masterclass in management watching him build another defence for the future. They're good enough despite their age to get games and get accustomed to playing in the first team, yet they're not old enough to expect to play week in, week out, making squad management in defence a lot easier. The defence is absolutely sorted for years now due to the experience the aforementioned youngsters have already got, though the individuals themselves also deserve a lot of credit. They are all amazingly talented, not to mention mentally strong. I must admit, after being very unsure of Evans after his amazing loan spell at Sunderland and first full season here, he can be very proud of how he's bounced back.
I'm still not sure what will happen with Jones, mind. Evans is too good to drop currently, and Rafael looks the superior and more consistent right back. It may rest on the fitness and progress of Fabio, funnily enough. If Fabio is fit, and the rest of the up and coming defenders progress as expected, then it'll be difficult for Jones. If Fabio stalls due to injury, I wouldn't be suprised to see this in the future:
Rafael Smalling Jones Evans
...just to somehow fit all three centre halves in. Evans has excelled at left back before, and is looking more and more comfortable on the ball these days.
Going a bit off-topic, but it's worth thinking about.
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