The most petty of niggles

What is it with English speakers adding 's' in inappropriate places?

TESCO is neither plural (unless you are talking about the 4 stores you had to visit to get bog roll) nor possessive, although Sainbury's is.

Lego is a mass noun, and has no plural. You have lots of lego, or many lego bricks. The official site even gets quite cross about 'Legos'

There is a road I used to live near 'Northfield Avenue' even some satnavs make it 'Northfields' which it IS NOT. (I even had to check the sign; my brother's satnav managed to gass light me)

ARGH the irritation. What is it that drives people to this?