As I understand the towers were completely rebuilt and guy wires replaced/upgraded within the last 8 years. It would have been 2007 or later as I noticed them running from Allston a lot on my way home driving down Rt 3. on the south shore during that rebuild period (no HD and rather weaker signal). There was info about it on fybush.com at the time.
They had to rebuild them in place to avoid disrupting the marsh they sit in. That couldn't have been cheap. The Hull site was built after Marconi died anyway.
For all anyone knows the outage was planned. Seeing it was a Sunday night that is likely. Knock them all you want for rare downtime, but aside from having one the best (if not the best) signals of the all the clears they are one of the few stations in the country to have an alternate transmitter site to keep the show going when working on the main to go along with the redundant transmitters at the main site.