Aaron, I just tested on a Natty live CD and apt:abiword opens in a small installer window, not in Software Center like it should. The bug is not that software cannot be installed with apt: shortcuts but that it doesn't happen in Software Center.
If apturl is uninstalled, apturl apt:abiword still works from the command line (but not in Firefox) and opens in Software Center so it is correct that SC has this feature working but apturl does not.
Aaron, I just tested on a Natty live CD and apt:abiword opens in a small installer window, not in Software Center like it should. The bug is not that software cannot be installed with apt: shortcuts but that it doesn't happen in Software Center.
If apturl is uninstalled, apturl apt:abiword still works from the command line (but not in Firefox) and opens in Software Center so it is correct that SC has this feature working but apturl does not.