Main reason I went with a freezer is the amount of kegs I can fit in it and the fact I can make it purdy for my finished basement. Many people have fridges, it's just a preference thing. Some of the fridges are pretty bad azz, especially the older ones.
My keezer is the 7.2 CF Frigidare. I can get 5 cornies in it, but I only have four taps. (Not to mention my Kenmore Kegerator that holds two more). It starts out small, then you always want more taps, I know I still do. It's a sickness.
I have a spare fridge sitting in the garage. Its my beer fridge. I strongly considered converting it to a kegerator, but there were 2 main issues I found with it (for my situation).
1. I didn't want to permanently damage the fridge. Unless I wanted to only use party taps, I'd have to drill through the door to add the Perlick taps. I didn't want to do that.
2. Size. Depending on how I built a shelf inside the fridge, I'm pretty sure I'd only be able to fit 3 kegs plus my CO2 tank. I have just started kegging, but I already know that I'll need more space than that.
Taking these things into consideration, I decided a keezer was best for me. I bought a Frigidaire 12.9 cu. ft. model for $329 (with a $50 rebate), and I can potentially fit 11 kegs in it with a collar. I don't ever plan on having 11 kegs, BUT I could. What I plan is to have 4-6 kegs at a time, plus several carboys for lagering or cold crashing, and some bottles.
By adding a collar, I can put the taps, gas line, and temp probe through the collar, so I don't actually have to permanently alter the freezer. If I ever quit brewing, I could take the collar off and simply have a normal chest freezer again.
That may not be important to some people, but it was to me. And it may end up being important to my wife, who hasn't seen the freezer in person yet, and also needed to be sold on its multiple functionality possibilities.