flashplugin-nonfree 10.0.15.3ubuntu1 is in Jaunty, which has the 64-bit version. This is not the same as flashplugin-nonfree 10.0.15.3ubuntu1~intrepid1 in Intrepid, which still has the 32-bit version. Bug 310061 tracks the 64-bit Intrepid backport request.
flashplugin-nonfree 10.0.15.3ubuntu1 is in Jaunty, which has the 64-bit version. This is not the same as flashplugin-nonfree 10.0.15. 3ubuntu1~ intrepid1 in Intrepid, which still has the 32-bit version. Bug 310061 tracks the 64-bit Intrepid backport request.