this is pretty incorrect, 64-bit applications are required only if more than 2 GB working memory should be used, which the vast majority of applications never will do. Actually 32-bit applications (and operating systems) do have a smaller foot step concerning memory resources/management and therefore are definitely to prefer for all applications not being a ‘memory hog’.
Win 10 x64 will of course run 32-bit applications without problems and Win 10 will be available as a 32-bit version too.