How the hell are you using your GPS when the car is in motion? The instructions totally said not to.
I don't work in maintenance and don't claim to be an expert, but there are a few factors at play here.
1) This is America, the most sue-happy country on the face of the earth. I'm NOT speaking from authority and I am completely speculating but my gut tells me that the manufacturers came up with these recommendations to cover themselves from liability (if... let's say a coaster saddles in a place where riders are stuck for hours and then they turn around and sue the park), and the parks obey these recommendations so if something does happen and someone tries to hold them liable they can turn around and pass that liability on to the manufacturer. If they didn't follow these recommendations, the manufacturer would likely tell them to go screw (sorry, that's a bit of complex legal jargon) and be absolved from liability.
I pulled that COMPLETELY out of my a**, but I feel like that's very likely what's going on here, especially because other countries who aren't as sue happy seem to have no issue running coasters in the dead of winter (hi, Japan!).
From what I can tell, the coasters can run fine if you don't mind a few close calls in morning testing, and the park thinks that the risk/reward is worth it if it means they can stay open 2 extra months and make a notable profit in November and December for (likely) the first time in their history. They likely don't think the event would be nearly as profitable without their coasters, and they're likely correct. Other parks have different philosophies but also appeal to different demographics and/or invest more heavily in non coaster related holiday offerings like shows / ice skating rinks / animal encounters / snow slides and things of that nature.
2) Unlike at Great Adventure, Six Flags New England's plan for running coasters in the winter is more involved than just hitting the dispatch button and hoping for the best. In addition to likely using harder / faster wheels, they use wheel heaters on all of their coasters for the event. I went into a little bit of detail elsewhere so I'll just quote my previous post in a different thread.
Joker and Mind Eraser had heat lamps in their stations. They weren't right on the wheels, but they warmed the temperature of the station overall which was nice for the riders, the people in the queue and for the train (as they were pointed at the train, just backed off 5 to 10 feet). Batman (their floorless coaster) had tons of huge lamps under the track pointed up at the floor mechanism and the wheels.
On a more interesting note, they brought out the heavy artillery on Thunderbolt (their classic, valley-prone wood coaster). They had an enormous (and I mean enormous) propane heater attached to a tube and a sheet metal vent system they built under the station that absolutely blasted the wheels with heat to the point that even sitting on the train waiting to dispatch was awesome since you were nice and toasty warm just sitting in the train despite the 31 degree temperature. They were monitoring the speed and if it ever ran slow they just waited a few extra minutes to send it while they blasted the entire thing with heat. It ran great.
Also, once a coaster gets warmed up it runs faster. There's a big difference between cold starting a coaster on a 27 degree night with a test run of an empty train and starting it with the sun out at 2 in the afternoon when it's likely 15 degrees warmer, running it all day which gets the wheels warmed up and causes it to speed up and then having it drop down to 27 degrees later on at which point the coasters has been running for 6 hours already... especially since it's running 1 train which means it's never parked on the block brake. It's ALWAYS either moving or sitting over heat lamps in the station so the wheels stay warm.