I didn't include this in my first reply because my food was getting cold and I didn't want my movie experience to be ruined by having cold food. My apologies. Do take what I'm about to say with a grain of salt though, as I researched this a while ago, so I could be wrong in some spots, but I can draw some conclusions.
A big part of CNC machining is the actual machine time. And usually what takes the longest is getting the big blocks of aluminum into the shape they need to be in, before cutting all the holes for vents, screws, etc. This machine time can make it more expensive, not to mention the aluminum that isn't used. So instead of a big block of aluminum that has to be cut to size, extrusion forms the aluminum into the general shape and size it needs to be in before any CNC work is done to it, saving time and aluminum.
This doesn't make the quality any worse though, as it's still solid aluminum and is still having CNC work done to it, but only the necessary CNC work.
TL;DR: You'll get the same quality for a lesser price because extrusion cuts down on CNC machine time
Of course, if Waha wants to elaborate he can, but I doubt he's going to settle for anything less than T1 quality, as he seems really picky with this stuff