Yes, dust is real. Canon is well aware of the problem of dust in lenses, and the significant impact it has on IQ. Many, many years ago, when they first decided to produce a professional zoom lens (the FD 80-210 f/5.6L), they designed and built a completely dust-proof prototype, hermetically sealed and assembled by engineering staff in a specially-constructed low-pressure chamber. When the photographic staff tested the prototype, which was given to them in extended position, they were surprised to find that as they retracted the zoom barrel, it got more and more difficult, the shorter the lens got. They talked to the engineers about the problem, and that team explained patiently that since the photography team had asked for - and received - a completely sealed lens, there was no way to equalize the pressure, so the lens needed to remain extended. They went on to say that they had the option to assemble the prototype such that the internal vacuum would tend to pull the lens either to the fully retracted or fully extended position, and they chose extended because 'more zoom is obviously better'. The photographic staff did agree that more zoom was better, but sent the engineers back to address the problem of not being able to keep the zoom lens at the wide end. The engineers bowed and went back to work, soon returning with a Mark II prototype. Their solution was a switch mechanism that would lock the zoom barrel in the retracted position. The photographic staff liked the solution - after all, they knew that zoom lenses are never quite long enough and never quite wide enough, so they are always used at one end or the other. At that point, the marketing team got wind of the project. They looked at the prototype and balked, claiming they could sell an 80-210mm zoom lens, but not an 80-or-210mm lens. They ordered the project scrapped, and the idea of a fully dust-proof zoom lens was abandoned. Marketing did have one final comment: "Keep that zoom lock thingy, we like that."
Thus, today there are still no dust-proof lenses, and yet we do have zoom lock switches, even on the brand new 24-70 II. True story.
Or, maybe not.