The only reason I can come up with, and sometimes this can be an important one, is that the dealers may know about TSBs from Subaru or other manufacturers whereas your less costly local mechanic does not get these TSBs.
On the other hand, having been a technical rep for a car factory, (not Subaru) I have run across quite a few dealers who received their TSBs from us, properly put them into a binder in the service manager's office so they could show me they had them when I came visiting, but never made any effort to get copies to the mechanics. Don't ask me why? Fortuneatly, a lot did make sure mechs got them.
I chewed out quite a few managers about things like this, but sure enough when I checked after another 5 or 6 visits, the bad dealers where back to their old bad habits.
Let me give you a hint on this. Every dealership runs according to the way the management of that dealership thinks. In other words, in the hundreds of dealers I have visited, across the US, the way things run always comes down from the top. Internally, the way the sales, service, parts and new car prep departments (and sometimes their used car dept if they have one) work will all be the same although they each their ways of covering up their deceptive practices if they are a "bad" dealer.
So my hint is this; when deciding about getting your car serviced, look into the other departments. Listen in to someone buying a new car, are they getting the run back and forth to the "New Car Manager" with every deal offer? Are the people in parts knowledgable and helpful, if anyone is picking up a new car, does it really seem ready to be picked up, any plactic stuck to the seat bottom edges? Are the people who work there content about what they are doing or do you hear people all over the place talking about being screwed by the boss? Are the telephones ringing endlessly and are they being answered in a cheery and "happy you called us" manner?
Of course, recognize there are days when no-one can be too happy and days when everyone is just overwhelmed.
Also, are the mechanics paid flat rate, or hourly? Flat rate mechanics, the most popular type, get paid x dollars, whatever it says in the flat rate book, no matter how little or how long the repair takes. If the book says 4 hours, you pay for 4 hours, the mech gets paid for 4 hours, the dealer gets paid for 4 hours. Dealer and mech usually split the labor money 50/50, sometimes a little different ratio like 60/40.
Good mechanics often make 8 to 10 or 12 hours a day. Bad mechanics sometimes make 20 or more hours a day. (Guess why?) Really bad mechanics often make less than 8 hours a day. In the extremely rare situation, an older, well experienced very competent mech may work slowly and do excellent work making less than 8 hours a day.
Feel out the dealer or local mechanic before getting repairs. It may take more than 1 visit.
Also, good rebuilt parts from reputable companies like NAPA and such are just as good or better than factory parts in most cases. Much better than 25 years ago if you had bad experiences in the old past and remember the earlier years when "rebuilt" meant opened up, looked over, obvious bad parts replaced, and shipped out.
Rebuilders are now factories just like your car manufacturer and every part gets the same "back to new" treatment, with rare exception with some junk brands.
RedCrow