Do I have to purchase OS X Mountain Lion before upgrading to Mavericks in Q4 2013?

I'm stoked about the pending release of OS X Mavericks later this year. A number of their improvements address concerns I've had in Lion that Mountain Lion didn't address.

I never took the time to upgrade from Lion (OS X 10.7.5 to be exact) to Mountain Lion earlier this year. Am curious if it's possible to bounce right to Mavericks later this year when Apple releases it, or if the upgrade path is strict for Lion users.

I know Mountain Lion will cost $20 for me to upgrade. I'm really just curious if Apple enforces a strict upgrade path.