>>>The title says it.
>>
>>Don't know for certain, but my guess would be the number of members that have read the message.
>
>Turns out you're right. Makes a difference to read it as the past tense as opposed to the usage as in the start of this sentence.

I can see that it may have some use as to whether a reply is warranted or not. But even in your example, it showed me that I was the first to read it, (or maybe that count doesn't include my current "reading", yet), but Michel had already responded to you by the time I entered my response.