If I may add only R$0.02 from Brazil here...
From my understanding in studying English (which I -- maybe incorrectly -- pride myself of being fluent in), pluralization depends on whether the noun is a countable or an uncountable one.
Bear with me for a moment.
For instance, you don't pluralize "rice" as "rices" because you don't care how many grains there are (and you would never be practically able to count them or even to use that measure for anything significant). So you don't count them as two, three or four rices. There's just rice. Same with coffee, sugar, sand or whatever uncountable thing you want.
OTOH, when you talk about countable things, you pluralize: Two eggs, four bricks, a dozen bananas.
So I don't think it's easy to come into consensus here. I tend to use "Lego" (BTW, in Brazil they're "Lego", not "Legos") because it 'looks' uncountable to me. But maybe some people see Lego more like "bricks", and I can certainly see some reason into that too.
Anyway, I don't really see an end to the discussion, but wanted to provide food for thought.
And yes, I realize I am throwing too much of a philosophy into a rather useless discussion. But hey, this is Slashdot.