I'm not too sure what the standard/consensus is - It's always up to the editors discretion. 
In my opinion it makes the map look quite cluttered and in this case it seems only 3 of the bike racks have rendered.

I believe there are websites that map bicycle parking, and if you are in a group of say 19 people, knowing that a single site has a capacity of 20 parking spaces would be better than having to count all 10 x2 parking spaces. :)