I have a 2005 Forester and just like the 2014 manual, it states that the middle is the least desirable location due to the seat cushion and some car seats not being able to be installed securely because of it (the wording almost looks identical!). But we were able to get both of our car seats to install in the middle without any wiggle or problems, using the LATCH system (we had a Chicco infant car seat with a detachable base and we now have a Sunshine Kids/Diono RadianXT). We also have 3 tether hooks (one for each back seat location), so it was clear to us that if the seat were able to be securely installed (less than 1 inch of wiggle) using the LATCH hooks, then it should be fine (because they put the tether hook for that position, as well). Also, both of our car seats had longer straps for the LATCH connections (meaning the LATCH hooks could be spaced a bit further apart -- we also only have 2 sets of LATCH hooks and use the two innermost hooks for the middle seat -- the same way we do in our Toyota Highlander). I never thought much about the length of the straps, until I recently helped a friend install a booster seat in her car that has really short LATCH straps. And I realized that her booster seat probably wouldn't work in the middle seat of our car (and she couldn't get it into the middle of hers, either -- even without a cushion issue, the straps just didn't reach when the seat was in the middle).
For us, the middle seat seemed safer (especially when he was rear facing) because, though the 2005 got great side-impact crash test reviews, it was before the side impact airbags/curtains were standard for the back seats in the Forester and I fear side-impacts a bit more in terms of the car crushing in on us (and hope/assume the car seat won't fail in a rear or any kind of impact, causing him to get ejected from the seat altogether).
One update, though... Just found this link while surfing: http://www.thecarseatlady.com/vehicles/the_latch_system_10.html
Basically, it looks like LATCH should not be used in the middle seat, even if the car seat allows for it (and it's a long list of manufacturers that are listed, too) -- so I guess we should have been using the seatbelt to secure it for all those years.