Source for this claim, please.
Spend some time over on the S&W forum. Issues with extensive use of full house 44 Magnums are well known and admitted to. Fact is that over on the S&W Forum the consensus is that someone who want's to shoot lots of 44 Magnums should just purchase a Ruger Blackhawk or super Blackhawk.
BTW, there are currently rumors that S&W has working prototypes of the 44 Magnum in the larger X frame and it's a 7 shooter. If it weren't for the mystique of Dirty Harry and his model 29, I expect that the X frame would be the only 44 Magnum made. However, that mystique is what keeps the model 29 and it's siblings in the catalog despite it's weaknesses. BTW, the model 19 also had issues with heavy use of the 357 Magnum and you won't find any K frame 357 Magnums in the current catalog, they've wisely moved that caliber to the L frame which was specifically designed for the 357 Magnum.
There are 2 critical weak points, neither of which present a safety issue in a range setting. However the issues with the cylinder stop dis-engaging during recoil could be a real problem in a Defensive situation.
One weakness is the Yoke tube is basically shared between the K, L, and N frames. The lengths vary but the diameter and wall thicknesses are shared. When you take a yoke tube that was originally designed for the 38 spl. and hammer it with a 44 Magnum it will peen even if it's using modern heat treated steel. Quite simply it just doesn't have enough "bearing area" to stand up to what the 44 Magnum can deliver.
The second weakness is the cylinder stop. Problems with this were so widespread that S&W redesigned the cylinder stop around 1988 in the so called "Endurance Package". Prior to the Endurance package the model 29 had a habit of unlocking the cylinder during recoil, and due to the twist direction of the rifling, the gun would twist in the hand enough to "throw" the cylinder back to the previous position. As a result a pull of the trigger would bring up the casing that had just fired. The solution implemented in the Endurance Package was a stronger cylinder stop spring in combination with longer cylinder stop cuts in the cylinder and a re-profiled cylinder stop. BTW, that did provide a total solution in a well maintained 44 Magnum, let that stop spring get weak due to lack of maintenance and I expect the cylinder will still unlock.
Pre Endurance Package 44 Magnums also tended to beat up the cylinder stops a bit more. However, with any revolver a lot of rapid fire DA shooting will eventually beat up the stop notches so it's really not worthy of consideration. IMO N frames beat up stop notches more than any of the smaller frames simply because the cylinder is larger and heavier. It's simply a product of the design that any owner has to accept and expect if he engages in a lot of rapid fire shooting.
Bottomline, the model 29 and it's siblings are GREAT 44 specials that can tolerate occasional use of the 44 Magnum. I'll also note that in Magnum Force Dirty Harry admitted to using a "light special" in his model 29, so even that movie character knew about the minor weakness of the model 29. BTW, it's not really a safety issue, it's simply a matter of End Shake developing more rapidly than desirable. My impression is that the End Shake will need checking every 1000 rounds and correction in the range of 2000 to 3000 rounds of 44 Magnum fired. Considering that commercial ammo in 44 Magnum runs between 0.80 and 1.00 dollar per round, it means you'll have to have your 1000 dollar handgun serviced for every 1500 to 3000 dollars of Magnum ammunition expended.
PS; I have yet to actually meet a 44 Magnum shooter who only uses that caliber in a S&W. Everyone I've met who has a model 29 or 629 mainly shoots 44 spl. or Magnum casings loaded to 44 spl. equivalent. Fact is that the recoil of the 44 magnum is a bit too stout for the average EXPERIENCED shooter to tolerate more that 20 or 30 rounds in a range session. However, with the 44 spl. it's a joy to shoot, especially in one with a longer barrel.