Wine absolutely can be a porting tool; Codeweavers offers porting services using this exact technology: http://www.codeweavers.com/services/

From a technical standpoint, Wine is extended to make the game work, that version of Wine is bundled with the application, and a script is included to run it without further user involvement.

I don't get why people still insist this sort of port somehow doesn't count. If it runs at full speed, shows up as a "Linux game" under Steam, and the user literally can't tell the difference, what does it matter?

Why does it matter if that compatibility layer sits in a system-wide library or in application code (as anyone would add if writing a program to target multiple kinds of system)? Wine is not an emulator, it's a free re-implementation of the windows API that runs on Linux.