Zyax - I think that you are getting confused because of a misunderstanding of sorts. There are several premises upon which Rolemaster is built, and it seems that you are missing one of the major ones.
The premise that you are missing is that Rolemaster expects that you will usually NOT be using 100% activity/OB in making attacks.
In most cases, you are expected to be parrying (i.e. fighting defensively), which lowers your OB.
Another premise is that you only get full OB if you 100% of the round in attacking (without parrying).
If you do anything else during the round, you OB gets lowered, based on the percentage of activity spent on those other tasks.
This is NOT considered to be penalizing the character. This is considered to be balancing things so that the player has to decide what percentage of his activity he devotes to what actions each round.
If he moves, that takes up some of his potential activity.
If he draws a weapon, that takes up some of his potential activity.
The character's skill bonus with his weapon is only the base from which his OB is determined. The percentage of activity put into the attack affects the OB, any weapon bonuses affect the OB, positional bonuses affect the OB, etc....
Look at it this way.....
A character's Base OB == weapon skill bonus - 50 + various mods
The Base OB is this because an attack
requires a
minimum of 50% of the character's activity in the round. You can then increase that OB by spending MORE of your available activity on the attack than what is required.
Rolemaster is not D&D, you do not get a Move Action and then a Standard Action (i.e. attack). You, instead, get more freedom to detail exactly what you are wanting to do, but in doing so, things will work very differently than they do in D&D.