Being from a farming family I realize the single most important piece of ANY durable good such as equipment....
DEALER Support
That being said, my local dealer REALLY took good care of me when I was fixing up an old F935 I picked up off a golf course....they treated me as if they sold me the machine way back in the day and went above & beyond for everything...example...within the first week (before I had my service manual) I needed some technical info...they graciously pulled a technician and helped me find the correct manual and page and then even photocopied it for me. The tech also gave me some tips & tricks... IMO none of that was "required" on their part....we were talking about a 18 year old tractor they never sold nor serviced. Natually my thought process when shopping for my new machine was, heck if they treated me that good on an old beater, imagine how they'll treat me on a shiny new one! Needless to say, this summer when shopping for a 35-40 HP Cabbed Machine, I got a great deal and was treated VERY good the entire time. Unfortunately since then that dealer has been bought up by a Mega store, so we'll see what happens. I'm not overly fond of the new mega store, but the people inside it are still the same. For now, I'm content with them.
SERIOUSLY Speaking, if the new mega store were to shaft me, I would seriously sell my 3520 Cab (with only 67 hours on it) and go buy a Massey or CaseIH cabbed tractor tomorrow morning because I'm now dealing with that CIH/MF Dealer for ANYTHING non JD Related because they give me the warm & fuzzies...not the cold box store feeling.... Box store already gave me the cold shoulder this summer when I was shopping for Snowblowers...
So back to your question, 2 big factors....the DEALER, and The "Heritage" of Deere, I feel Deere isnt gonna go anywhere so in 15 years when I need filters and other parts for my Deere, Deere will still be there to support it. All that being said, CAT has been around forever too, but I'd NEVER buy a CAT tractor because of the dealer model they choose to use.