If it is true that officially, the karma limit is raised to 50, but effectively, the actual programming behind this "blog" allows for anyone to post at 20, then it suggests a real inconsistency between stated policy and actual policy.

Inconsistency is certainly not good if people want to actually follow policy. Either the official karma limit lowers to 20, or the real karma limit goes to 50. I lean towards the latter, because the existence of the Discussion section obsoletes the existence of the main LessWrong section, but the fact that this stated policy was formally established in 2009 suggests that there might have been policy problems detected by the staff that prevented it from becoming actual policy by this time (maybe the inability of most people to reach that high total of 50 that forced the staff to not implement this policy before).