That's a new one one me - though I only ever submit data for manufacturing in Gerber format, which every PCB manufacturer can accept. I'm not sure I (or my customers) would be too happy about releasing the original CAD source file anyway.
In fact I'm quite surprised to hear of any PCB vendor directly accepting the native format of the CAD software used to design the board. How do they know which items from which layers are to appear on the board, and which are unwanted / documentation only? Does Altium have very clearly defined separation between items which always form part of the finished board, and items which don't?
(In Cadence I have to define the set of artwork plots which form the layers of the board, along the lines of: to generate 'top copper layer 1', draw the pads from layer 1, shapes from layer 1, text from layer 1, vias from layer 1, and various other items which I want to appear on all layers by way of documentation, such as a copyright notice and alignment targets).
If I were choosing a CAD tool right now, I wouldn't even give the issue of output format a moment's thought. Every PCB tool can generate Gerber, and every PCB manufacturer can use it. They may also share other formats in common, but for me at least, the ability to send the raw CAD data to a Chinese board manufacturer is so far down the 'nice to have' list that it doesn't even register. I'm not sure it even qualifies as 'nice'.