Double standards of companies while hiring

I am highly annoyed by double standards and hypocritic behavior of companies while hiring for Notice period. Almost every company wants immediate joining or asap joining and they will definitely ask or encourage you to negotiate notice period, etc. However they themselves would not have allowed a single employee to leave early or waive off notice period. I sometimes feel to ask them, that i am sure the employee who's replacement or position i am being hired for would have also asked to waive off notice period, did you allow him/her? If no, then why do you expect another employer would do something different. I mean, my current employer asked me to negotiate notice period when i was leaving my previous organization, now if tomorrow i resign, i know they won't waive off a single day. If anyone else have good experiences, answers around the same. Please do share.