Why don't take into account slipways on a river boat map ?

[fab-girard]

Hello,
slipways :
http://wiki.openstreetmap.org/wiki/Tag:leisure%3Dslipway
http://wiki.openstreetmap.org/wiki/Tag:emergency%3Dslipway
seem not be taken into account in Open River Boat Map. As you process for port/marina, I think slipways should be visible even with a large view : it is a good indication for existing waterways or not. I many places, there are slipways without marina...

Fabien