From a purely commercial viewpoint, my view is that if you returned a faulty cable, or unit it connects to, with adhesive residue on it, any supplier would be within his rights to say "warranty void due to abuse". As Mr Church says, it screws cables but perhaps more importantly it attacks the electrical connection like acid.
Of course, I don't care what people use... I prefer to use velcro whenever possible. But some things can only be reasonably done with gaffer tape. Like attaching a battery securely to a v3.
What you describe sounds like a company looking for an excuse to void a warranty. Residue doesn't kill gear. Who puts tape on electrical contacts? That would be a different case, and extreme example. That is one of the design faults of minijacks - the contacts are exposed, most commonly to finger oils.
Look at gaffer tape use in the film making industry. When they are paying hundreds of thousands of dollars per hour (or in extreme cases, millions per shot), you employ people whose sole function is to gaffer tape the hell out of everything.
And with gaffer tape, residue is not likely unless the tape has been in place for more than 1.5 years (depending on environment). The other case where residue might become a problem is when the heat has been somewhat extreme. Inside a bag in summer, with hot gear, there can be temps that exceed the temp range for gaffer tape adhesive. If you remove the tape under those conditions, the adhesive does not stay cohesive, and there can be residue.
I put gaffer tape on my cameras to improve the grip. If you pinch it and stick it to itself, you can even create little ridges. I also put it in high wear spots to prevent wear. The head of my Gitzo tripod is covered in gaffer tape to prevent nicks from rocks and other objects.
One of the neat things about GT is how many times I can re-use a piece. I'll stick my "spares" on the surface of my dvd batteries, or on the legs of a stand.
Fwiw, I use common "duct tape" for almost nothing. Hate the stuff, and the nasty adhesive. Proper "duct tape", made of aluminum sheet, is neat stuff and useful for some situations where nothing else will really do. It also tends to do well when subjected to moderate heat, because of the intended use on hot ducts. Though I don't think I have ever used it with my recording gear.