Not enough keys to go around. I worry about the case where the developer builds in a lot of single key access and that the user inadvertently activates functionalities. You could have some single-key defaults. Tricky on a smaller keyboard like Intellikeys or switching devices. People with motor disabilities.
Single key can be tricky since so few keys.
Opera allows him to jump from header to header with a single letter key. Or link to link in IE or Lynx. You need to be able to configure access. You may have a strong need to include single key access. We didn't mean that configuration had to be single stroke but rather that one be able to activate important functionalities with a preferred keystroke.