Perhaps a more apt comparison is to the word 'brick', since that is what Lego manufactures.

In my experience (US), the usage can go either way. A house built of bricks (multiple building blocks) or built of brick (general building material).

Ok- now that I've written it out it seems a silly point to make. Bricks, logs, blocks, plenty of options all with the same "rules".

Ah well, hooray for variety! It's the differences that make life interesting.