How do you know they deleted their posts and got downgraded as opposed to them having the potential activity to be a senior member and that thus awarded them the merit...
The initial merit is not based on potential activity. It's the "minimum required to your rank". Nikisa is correct,
IF flash101k was a member when the merit system was introduced, he would only have 10 initial merit instead of 250.
For current members, your initial merit score is equal to the minimum required to your rank.