Fender is the most represented brand is basses/guitars for several reasons. First I'd say tradition; its been a major brand since the beginning.
And they have some good advertisements and invest good money in publicity (Which I believe is the major factor).
Also since they are such a huge firm they can afford to have a broad selection of instruments in a broad price range and still have at least decent quality.
I agree with you and the OP for 90% of what youve said. Tradition and the "its a Fender" thing are probably the biggest reasons people buy them. The fact that Fender basses are the ones we've all seen since birth it's kind of ingrained in our minds that that is the definition of what a bass is. Again I agree that marketing has greatly contributed to this as well.
I have to disagree with the last point in terms of "broad selection". Fender, like Gibson, is notorious for making a pick up swap, calling it a new model, and charging us an extra $500-$600 for it. At the end of the day they only make four basses, one of which almost doesn't count (Bronco).
You would be hard pressed to find a broader range of "off the shelf" basses than Ibanez's offerings: Bolt ons, neck throughs, solid bodies, hollow bodies, double cutaways, single cuts, active electronics, passive electronics, etc... I know a lot of "elitists" look down on Ibanez for whatever reason (its not a Fender?) but they really do have a lot to offer, and playability is always high on the list.
Now don't get me wrong I like Fender basses, P-Bass Specials being my fave, but I am also kinda tired of the "Kool-Aid" so to speak. There is a certain vibe to a P bass, and a certain sound, however my Carvin LB76 just offers far more versatility both in playability and tone than anything with a Fender logo.
In all honesty it is true that far too many engineers and musicians hear with their eyes. As a player you can either fight it, or just realize at some point in your career you will show up to an audition, or recording session with your "modern" bass, and they will ask "don't you have a Jazz?" A bass is a tool and missing a P or J in your arsenal is like missing a hammer or screwdriver out of your tool box. You can get by with out it, but having the right tool for the job makes life so much easier. This doesn't mean you have to drop two grand to get one, just buy a MIM or Squier and be done with it.
The bottom line is this: Use whatever makes YOU happy or anything that will help you land the gig/recording. If you don't like Fender, or don't buy into the "Fender is God" thing thats perfectly ok. Don't buy one. Just realize that some people DID buy into it and it may close a few doors if you don't have those bases or their boutique counterparts. It's stupid and I don't agree with the thought process, but it happens.
Well there's my dos centavos and keep on

no matter what bass you use.