Again, you're falling back on old advertising claims. I'll give you that one of those revolvers probably wouldn't blow up from shooting .38/44 ammo, but I very much doubt that it would hold up well to continuous shooting with thousands upon thousands of rounds of it like it would with standard pressure .38 Special ammo.
Of course, Colt and S&W probably assumed that no one would be foolish enough (or have a high enough pain tolerance considering the factory grips) to shoot .38/44 ammo continuously. More likely, the average person would shoot a box or two of .38/44 ammo every now and then and practice primarily with standard .38 Special ammo. Of course, one cannot make such assumptions today because too many people expect their guns to be able to handle a steady diet of nothing but full-power ammunition.
There are a few of problems with this statement. Number one is that a M10 from the late 50's and a M&P from the early 20's are not the same thing (and if it was indeed a M10 then it could not have been produced before the late 50's). Secondly, in the grand scheme of things 1,000 rounds really isn't all that much. Neither you, I, nor your cop friend knows what condition that revolver might have been in had he fired 5,000 or 10,000 rounds of .38/44 ammo. Finally, your friend was using a fairly new gun at the time. The vast majority of 1950's or older vintage revolvers out there today have been resold multiple times and there not much way to tell how much of what kind of ammo the previous owner(s) shot through them.
It's an advertisement and it doesn't prove anything. You say that the advertised velocities were 5-10% inflated, well I'm sorry but I'm going to need a little more than "in my experience" to believe that. Show me some independant third-party chronograph data comparing vintage and current ammo through a single revolver with a reasonable barrel length and then we'll talk. Until then, I don't much care what old advertisements say because there's no way to verify the claims.
Your understanding of the relationship between pressure and velocity is obviously very limited. It's not as simple as higher pressure=higher velocity. SAAMI rates ammo according to peak pressure, but peak pressure does not directly correlate with velocity. Just as important, if not more so, is how long that peak pressure can be maintained. Fast buring powders reach their peak pressure quickly, but that pressure also falls off quickly and, conversely, slow burning powders don't reach peak pressure as fast but the pressure also doesn't fall off as quickly. This is why slow-burning powders are better for long barrels and fast burning powders are more suitable to short barrels: a short barrel needs peak pressure to be reached quickly to attain maximum velocity while a long barrel needs peak pressure to be maintained as long as possible. So long as people aren't paying attention to what barrel length or type you're testing from, it probably wouldn't be that hard to get impressive velocity figures without being overpressure by simply loading the case full of very slow burning powder. The problem is, that the barrel necessary to get those velocities would be so long that it wouldn't be comparable to any common service sized revolver.