lost some one time revenue, probably gain more long time
While it will take time to bear out success or not with this new strategy, i think it's a pretty good strategic plan.
My estimation of what apple COULD have generated from a mavericks 20$ upgrade price was MAYBE 500-600 million all in, over time which could be a couple years to realize if at all. they could have probably gotten 200-300 million in the next 90 days, the rest over the following 18-24 months.
Now, with the upgrade to mavericks, it enables a number of things that just might drive users to subscribe to other apple services and would most likely remain subscribers over time.
things like itunes radio, via music match mostly. 25$ a year
increased storage for icloud, for either music syncing or overall backup and storage that starts at 20$ a year and quickly goes to 40/50$ a year.
The integration of apps (which are pretty much being given away for free now) icloud reminders, settings, safari etc across devices could even enhance the halo effect that apple already gets for people to buy ipads/iphones/minis, etc..
So, it's probably a short term loss of revenue (which honestly for apple is a rounding error) but an higher possibility of LONG TERM revenue enhancements
AND they get all that media attention "It's FREE, FREE FREE!" and good will from customers.