As far as the total achievements go, I think it is a true sum of all the instances of each achievement. However, next to each achievement, it only shows the most significant power of two in the binary representation. So, if you have 70 +5 posts, it will only show 2^6 next to that achievement, but will contribute the full 70 points to the total.
"We Americans, we're a simple people... but piss us off, and we'll bomb your cities." -- Robin Williams, _Good Morning Vietnam_