If you do the math,, no, you are not paying more and more, you are actually paying less.
Even if it is on one PC for the Office 365 subscription, it's works out to being cheaper if they upgrade it each year with new features ala Blue, this is still up in the air as no info has been released about it officially.
Again,,, Retail 400$+ right now, or,,, $400 over 4 years.
If a new release is out every 3 years, it's actually 300$. per release
But not everyone has only one PC, so, the more you install it on, the cheaper it is.
So,
$400 x 5 = $2000
or
$100 / 5 = $20
Basic math is fun