There are only two things missing in FS2_open that aren't in FS2. That's the MVE playing code and the PXO stuff.
Until I converted the avi's not being able to play the MVE files was a good reason to use FS2 1.2 If you wanted to replay the main campaign you wouldn't get to see the cutscenes.
However now that the cutscenes have been converted there's no good reason to use FS2 1.2 any more for the main campaign. FS2_open will play the movies just as well as FS2 did (better in fact since now they play off the HD without asking for the CDs). You get to see all the cutscenes in the right places but now you also get the improvements that FS2_open made to the game.
Secondly Fractux's server is limited in the number of people it can serve at any one time. The avi files take up 134 Meg in total. The MVE files take up 4 times that amount. If they were uploaded it would mean that traffic on the server for the movies would become 4 times as bad.
As it is I see people complaining that they can't connect. I'm not about to upload something that will make things 5 times worse just because some people can't be bothered to spend 5 minutes downloading and setting up FS2_open.