Most of my basses are Fender. Hell, almost all of my basses are Fender. I only own 5 non-Fender basses currently, and one of them is a G&L.
I use a P-bass because my first bass (still have it and its my main player) was/is a Fender P-Bass. Its what I'm used to, and what I like. I also do a fair bit of studio work, and the most requested bass is one of my P-basses. They sit will in most given mixes with minimal tweaking and I do a lot of reggae, dub, soul, R&B, hip hop, funk, and dance music so a P-bass with flats usually fits right in. Occasionally I'll use a Jazz bass with flats or something but the P-bass is clearly king here. I play in rock bands, I play jazz gigs, and do as much as I can with as many people as I can.
Ampeg? Eh....
I've owned a lot of their stuff in the past. I currently own an SVT-3Pro head and the SVT-VR. The 3Pro is the smallest amp I own, and I pretty much use it as a practice/small gig amp. I don't use the VR, even though I'd like to because its broken and I can't afford to fix it.
I usually grab my GK 2001RB or my Mesa Boogie 400+ for live stuff. Way way more wattage and headroom. Both amps sound really good to boot. Regardless, I still sound like me no matter what rig I'm playing through. Some amps are better for different applications though.
Almost all of my cabinets are Ampeg though. I like them. They're cheap and they're durable. I've got 5 Ampeg cabinets currently, and two Bergantino. I can pretty much nail whatever it is that I'm going for between either of them.
Do I discount other stuff? Hell no! Do I use Fender and Ampeg? Well I'll give you a hell yeah with various degrees of satisfaction. Both companies still dominate a fair share of the market place and they're what you see most often.
All said, I still want some more G&Ls, a Ray, and something fancy with Soap Bars.