I believe this is part of the theory behind the ABCDE diet and thus also partly behind the theory of T-mag’s own revision of it, the delta 1250 (probably even behind the growth surge project as well). However, implied in each diet is the idea that fat will likely be gained on massing periods and muscle will perhaps be lost on cutting phases. This gives the following cycle more importance to reverse the damage of the preceding one.
I think that many people will attest to continuing gains for long periods of time doing nothing different with either training or diet, however, as I think Ian king might say, we need to make the distinction between what is possible and what is optimal.
Certainly you would change your training parameters before ten weeks have passed on a massing phase and many people have gotten great results keeping diet relatively constant while only manipulating training for long periods of time.
I think that if you can do a massing phase carefully like, for instance, Marc McDougal without gaining fat, then their seems to be little reason to change the diet. However, most people will probably gain some fat and find it helpful to lower intake for a period of a week or more. Indeed many people might make what they think is poor progress after an extended period of intense training and eating in which case a change seems mandatory.
Your own results should probably determine what changes, if any, you should make. I do think that if you were to continue eating in the same way for a long period of time you could well benefit from a change. Proper training stimulus and caloric surplus might be the most important factors of gaining size, but proper variation of diet in conjunction with training might provide the very best conditions and stimulus for growth (in addition to keeping you lean while doing it).
I would love to hear what others think about these cyclical manipulations and theory.