In the end, it doesn't. It usually happens accidentally, and it is often useful information to the poster that the person they quoted may not be active on the site anymore and thus will not respond. That was the reasoning for my first response, and is consistent with how others have dealt with like situations on this site and elsewhere (and people generally respond with something along the lines of 'whoops, thanks,' or 'no, I realized, I still wanted to respond, it's okay if they're long gone'). The second was more bemused response to the evasion. As you say, it doesn't matter, and thus being evasive in the response seems unnecessary and unusual.
Then why can't you say whether you noticed or not?
To the subject at hand -- if the DM has an idea of how big their giant (or dragon, etc.) is, then knowing how much that equates to in weight certainly has value (so kudos to the books and everyone who provided answers for doing so). On a broader level, even in editions where the size (or at least height/length for dragons) was listed, I don't think any two people ever had the same conception on how big these big things were, certainly not until something like whether they could fit somewhere or could they be pushed off of something came into play. It seems that sometimes the devs (or at least artists) had similar problems. There's many instances of artwork where the giants seem wildly larger than their book descriptions, and at least one instance in the writing (in the Orcs of Thar, I believe, ogres are said to play a game where they see how many halflings they can fit in their mouth). Not that that means much for giants adhering to the book standards, but probably a good idea with a new DM to confirm how they envision their big entities.
It's a fun read if you have the issue or can find a PDF online.
