This is something I haven't heard anyone mention, but seems probable. With the Rockstar online scheme leaning toward making virtual payments on your property (insurance for instance), it would make sense for them financially if we were forced to pay rent on our safehouses in-game rather than buy them outright. This could be the reason that they are often referred to as "apartments" as well, since apartments almost always specifies a rented property rather than a home, which is owned. This would be smart for Rockstar financially, as it would mean more money in "cash packs" if they are actually going to a micro transaction future.
Just a semi-logical thought I had. What do you guys think?