Seems there were issues with the bridge coming up at the edge's, no pun intended. The Support Local Musicians is one way to tell the difference betweend the EA40 (older) Washburn and the EA20 (used during the Zoo tours).
While the both the EA40 and EA20's came with a piezo pickup in the bridge, Edge went a step further having the Lawrence soundhole pickup installed.
Piezo pickups alone, in an acoustic can sound a bit tinny and shrill. They don't pick up the body sound of the guitar. Hence, the soundhole pickup. You get more body to the sound.
Piezo's being thin in sound can be good to get definition but not a full sound.
Many acoustic electrics made today, certainly the more quality models, have a piezo in the bridge and another mic-type pickup inside the body. Taylor has a "blender" EQ system where you can use the piezo, the internal mic or blend in the sound of both.
Think of it as having a woofer and tweater, like a speaker (for highs and lows) and hence a blend of full spectrum of tones is available.
That said, some of the under saddle/bridge pickups but LR Baggs are far better than the piezo's of yesteryear. The LR Baggs systems are in the Pete Townshend model SJ200 (used on acoustic performances of "Stuck in a Moment...") and in the Goodall acoustic that Edge is seen playing on the acoustic version of "Sometimes You Can't Make It..." on the DVD included with the HTDAAB deluxe edition.