I'm sure someone from AP will provide a more comprehensive answer (they have before; I tried to search for the posts but couldn't find them), but until they do I'll remind you that the approach plates and airport diagrams are now geo-referenced, when prior to v6 they were not. Originally, the FAA was going to include the geo-ref data with those charts for free, but earlier this year they announced they would not be doing that after all.
AP had been counting on the FAA data, and had to scramble when the FAA pulled the rug out from under them. AP selected a 3rd-party geo-ref data provider, but that 3rd party charges for those data, and AP has to pass those charges on to us.
Despite the fact that I cannot find the messages now, this coming price increase has been discussed on the forums more than once, and I received at least a couple of emails from AP alerting me to the price increase. To ease the transition, AP had continued to hold the price at the $89 level for several weeks after v6 was released and encouraged current subscribers to re-up at that rate before the new price took effect.
EDIT: Here's a post from Walter with info on changes to the VFR and IFR subscription packages, including rationale for the price increase: ifly.adventurepilot.com/SUPPORT/Forum...