SUID bit in file permissions

hi all, this is regarding the SUID and SGID bits in permissions of files in linux. some files have the SUID set in the 'x' part of the first 'rwx' (that is, the user's permission field). i have read that setting the SUID bit enables the file to be executed with the owner permission and not with the permission of the user executing it. now, what is the difference between setting the SUID bit and giving execute permission to 'others'? do they not both achieve the same purpose of enabling 'others' to execute the file? i think this is a silly question...but still, wanted to know...