What about this exactly is propietary?
Air runtime = free
Flash player = free & parts of it open sourced through mozilla
Flex SDK (for creating flash applications) = free & open source
Flash remoting (blaze ds) = free & open source
Creating html/ajax = free
Sql lite = free
pdf = open standard
Flex Builder and Creative Suite, which are quite proprietary. And most certainly not free (costing up to $700 and $1800 respectively).
Just like PDF is, as you say, an open standard and Acrobat Reader is free... but Acrobat Pro is startlingly expensive.