US & CA Plugs
The north American plugs and sockets are very compact but the tolerances are very poor, so it's pointless for a device to rely on live and neutral being correctly connected, as the wider blade universally seems to fit into the narrower slot, unless there is an earth pin.
Plus the majority of device plugs are earthless, even if the earthed version is already substantially more compact than either UK or European earthed plugs. If everything over - say 100W - was earthed, that would start to promote a higher standard. Adopting earthed plugs universally on US&CA devices universally would be a better move, as there are knock-on effects of using a ('non-polarised') 2-pin plug as standard. Firstly it drives unrealistic expectations on the size of products containing integrated plugs: if a product is designed to have 2 flat blades protruding, it's more difficult to adapt to larger EU and UK plugs. Secondly, for products with a power cord, there have been many last minute 'gotcha's' when trying to fit an EU or UK plug into packaging designed for a US 2-prong.