411A's nailed it. (Cheezes cripes, man; you seem to have flown a lotta different planes, eh?)
Lack of thrust/power is it. Nuthin' fancy 'bout it!
I only fly the DHC8, and cannot speak on behalf of any jets, but I tried both techniques the other day -ENBO-ENEV-ENBO- with the *exact* same TOM (OK -granted, 'twas a few pounds +/-, but not than many!). The "step" method (when approved by ATC, of course) used about 10-15sec longer to reach cruise TAS, as opposed to just levelling off and waiting for cruise TAS, maintaining climb power of course... It'sjust a matter of energy management. The psychological effect is the greater...
Modern aircraft have no problems with power/thrust vs. power/thrust req'd, and hence the "step" is just a load 'o bollocks...