Hi, dippi!
The upgrade is not complex or what ever - it is pure marketing. The stick with the basic version costs about 40,10 €, stick and plus version 72 € and plus version without the stick (the upgrade) 43,20 €. For some users the full version might be to expensive - or at least MULTIPLEX officials might think so. For me it was clear right form the moment I got interested to buy the full version.
So it is with many products in the RC-business: producers offer limited versions and full versions, customers buy the limited version because they say they don't need all the features. Later they see the full version would have been the better choice. Is it the same with you and the MULTIflight?
w/r
profimc