MACMAGNA Yes sometimes applications could be uninstalled by just trashing them to the trash and sometimes not. I think you have to post the same comment for the popular AppZapper ( http://www.macupdate.com/info.php/id/20306 ) which do exactely what you suggest for $12.95 and like you miss some files, package receipts, custom libraries, private frameworks, tmp files, log files, hidden files, etc... when "uninstalling" an application. Uninstaller do more than just searching for some name related files in some basic folders: Uninstaller compares file system hierarchies item by item and can also be used to find changes in any folder or disk of your choice between two dates.
Additionally, i suggest you first download and test the shareware before posting a comment on it. This does not apply only to Uninstaller, of course.
(Version 1.10.5)