Clinton, you must be thinking of those god-awful plastic-y finishes you sometimes see on cheap guitars. It's true those guitars sound awful, and don't improve with age, but they're just bad guitars, badly finished.

But it doesn't follow at all that satin-finished guitars are superior to gloss-finished guitars. A good shellac (french polished) or lacquer finished guitar does indeed "open up" with age (well, not age really, being played is what does the trick).

The advantage of the satin-finished Seagulls is that you pay less than you would for the same guitar with a good quality gloss finish -- it's cheaper to manufacture, that's all.