It's not a "dumbing-down" thing. If you've ever had a broadcast gig, you quickly find that if you're on the air, having a small set of repeating catchphrases and statements helps you to be quicker on the microphone when they point to you. Trying to think of something intelligent and cogent on the spur of the moment at the pace that broadcasts go is an exceptionally rare skill, so a "Holy Jumpin'!" or a "pepperoni pizza" serves as a ready-made crutch in a high-pressure, high-paced environment.
IIRC, Tyson had it pretty rough when he first started doing color commentary, and his natural ease with talking and chirping was nowhere to be found. It took him a while to find his groove, and it wasn't until he got his shorthand down that he started to sound at ease.
Lyndsey Fry had the same issues when she started, and she's adopted a couple of shorthand crutches of her own now, but she plays it straight and not the "dressing room jester" that Nash sometimes tries to be.