This isn't the first time this has happened. This isn't even the second. The new seasons always began in November from the beginning up till Season 31, which ended up getting delayed a couple of months; after that, new seasons began in January up till Season 34. From then till Season 37, new seasons began in April, then 37 was delayed till August. Season 40 was held off till November 10 in honor of SST's first broadcast on that date in 1969; since then, new seasons began in September.
Again, this sudden HBO deals seems to have made waves, and I'm sure it's causing a lot of crazy changes behind the scenes regarding the show and its broadcast.