Gravity is a problem for N American plugs but not for Euro or Schucko plugs in Schucko sockets. This is what they have in Germany and the Netherlands. The plugs fit in snugly and do not move. If you don't push in enough to "lock" in then a spring (or something) pushes the plug back out. So it is very obvious when it is in correctly and basically can't be partially plugged in. Gravity has no impact on the plugs in my house whatsoever.
The Schucko plug/socket system is very robust, safe, and well designed.
Not only that, also gravity pulling on the cable naturally tends to pull European and North American plugs out of their sockets, whereas this angled design in UK plugs prevents that.