There is no "right" or "wrong" on it, honestly. There is the preferred usage by the company "LEGO" for the collective noun. You can say that is correct or you can say that it is what it is ... a preferred usage to ensure a trademark.

The way people differ in using it seems to be entirely based upon how they view the item, it seems. But I think the reason Americans use LEGOs rather than the collective noun is because we shorten things. For instance:

So far everyone has been saying, "LEGO brick/s" "LEGO piece/s" "LEGO set/s" and so on and apparently we can agree on that. Everyone above has said that's fine, at least. And each time the modifier to LEGO is pluralized by an "s".

"LEGO brick" / "LEGO bricks". Obviously the "s" changes the singular "brick" to "bricks". So, Americans dropped "brick" altogether, deciding to refer to each brick as LEGO, and carried the "s" over as a plural substitution. We don't see a "LEGO brick" necessarily; we see a "LEGO". When we use the word "LEGO" we are implying "brick". Thus, when we say "LEGOs" what we're implying are "LEGO bricks".