You seem to forget that I never said that ECL = HD + special abilities. That was something that you came up with. All that I stated was a rule which says "an ECL must be greater than or equal to the number of HD that a creature has."
You also seem to have misunderstood what I was saying. I should probably clarify that this rule doesn't mean that each HD = +1 ECL. Even Soldarin's ECL Calculator takes into account that each type of HD isn't "worth" as much as other HDs or class levels. IIRC, his sytsem calculates each HD as 1/3 of an ECL. However, the rule still stands that the final ECL must be greater than or equal to HD. A 3 HD creature may have a total ECL of +4, of which only 1 out of the 4 points of ECL is HD-related.
In the end, what ECL represents is "this is the level in which the creature's abilities won't be overpowered when compared to the rest of the party." It isn't able to make a monster character exactly equal to a character of the same level. An ECL +6 monster Ftr4 won't be as good as a Human Fighter10. They simply don't have the experience or training of the 10th level character. However, the monster's racial abilities ought to help close most of the gap.
But as it stands now, if you want to play a monster character, you will have to accept some drawbacks along with that. Namely, a lack of class abilites, BAB, saves, and HPs. Is that fair? Maybe, maybe not... In the end, it's up to the individual DM. If they feel that the published ECLs for a troll is too high, they are free to say that trolls are ECL +1 or whatever they feel like. The way that I see it, the current ECLs are merely rough guidelines. They most likely haven't been thoroughly playtested, so it's up to the DMs to decide if they are balanced.