Ideally there would be(there is heat treatment in aluminum out of necessity) but the cro-mo tubing is made specificly to not need it as much, allowing them to forego that step. Some of the newer alloys are what they call air-hardened, negating the need altogether.
This is also why the fillet brazed stuff is still regarded as the ideal construction means for steel. Everywhere there is a weld junction there will be different stresses which can create problems later in the way of fatigue. Thus in fillet brazing the temperature is much lower and the joint, being bronze, has a certain resiliency that reduces the fatigue factor. On my Giant frame the front triangle is tig welded and the rear and accesory mounts are brazed. The extent of the heat treatment usually used in steelwork that I have been taught at school and elsewhere is merely to normalize it by torching it evenly around the joint and letting it cool.