That may have been because in RoCo II the skill was optional and IIRC offered no additional value to the game. It was just another skill you needed to invest DPs into if you wanted to have Power Points. With RMSS it was part of the system - so that you could not evade it - plus RMSS changed the number of PPs developed per level, so that a spell caster had more PPs at his disposal.
Actually, when using the RoCo rule, a spell caster would usually have way more PPs at his disposal than otherwise.
1) Base PPs,
2) Two skill ranks per level,
3) Die roll for each rank to determine the number of PPs,
4) Multiplication using the stat.
For instance, with a stat. of 100, the number of PPs is 3, so a level 10 using SL rules has 30 PPs. With the RoCo II option, he has:
1) 10 base PPs,
2) Assuming two ranks per level, he has twenty ranks in PPDev,
3) Assuming a d5 for each rank, thus 20d5 = an average of 60 (but usually probably better as all skilled GMs/players know to choose/roll his dice to help luck
),
4) Assuming a +25 stat mod (the normal figure for a 100 stat), we'd have to multiply by 1.25,
5) The total would be: (10 + 60) x 1.25 = 88!
...and let's not imagine the case of a magical race using a better PP die, or a race or character with a bonus to his stat mod... I've seen players rolling (at level 10) a total of about 80, using the option of adding +15 to their stats, and with a racial bonus of +5; at level ten, such characters have a whooping (10 + 80) x 1.45 = 131 PPs...
So, sure, it's another skill into which to pour your dev. points but let's say that the perspective to have four times more PPs is really... motivating.