Well, fortunately, most of those update replace files and not "add to" the files in the system.
I do agree that Windows is all updates.
I am running Windows 10 TP on my Pro 3 now and seems to work pretty good but the USB port is still underpowered.
OS/X has updates as well but only a few, here and there.
Linux, however, gets a lot of updates on its own but you have like 200 updates but they download/install in about 5 minutes maximum. That system is now in par in size as Windows.
Updates are inevitable. As long as you have hackers out there, they are going to be constant.
In the future, I do believe that Microsoft will drop the number from "Windows" and just Windows and like you mentioned, it will be a subscription service much like Office 365 is for Office. However, that is multiple machines for one price per month or year.
An example for cost; Microsoft usually released a new version of Office every 3 to 5 years. They charged a big price for a single license which can be re-installed up to 5 times in case the machine got wiped out. That single price could actually pay for
a constant new version of Office in 7 to 10 years time frame. Windows will probably work in that same fashion.
They are planning on keeping Windows 10 Technical Preview even beyond the RTM release date. They are talking of keeping it 'beta' almost forever. Even though Windows 10 Final would be out on July 29th, the beta version keeps going and continues to get
upgrades beyond the RTM version. That is the concept I read about.