[panacea]

Lego is a medium. Like paint or sand. No need to pluralise :-)

[davidw]

It's a fairly fluid concept. In Italian, for instance, spaghetti and capelli ("hairs") are both plurals, rather than their "uncountable" English equivalents. I.e. "We're having spaghettis for dinner, but first comb your hairs".

I always played with "Legos" as a kid, so for me that's what they are.