Eddy... sorry to disagree...
The real admin can delete users with admin rights. Other way around is not possible.
Users with admin account could do it too... I've done some times...
If you login as user with admin rights and the system gets infected, it may be able to disable ALL user accounts. In that case only the real admin can restore things. (this is btw a good reason to always use a limited account unless there are specific admin rights needed to do a task)
But you're comparing the 'real' administrator account with accounts with admin rights and NOT the common user.
Logging with the Adminstrator account OR the account with admin rights will be the same in this case... all users accounts could be 'messed' according to your words...
The real admin can set rules/settings even a user with admin rights can not do.
Just set 'special' permitions and the accounts will be the same...
But, after all, there is NO difference (and shouldn't have any) on installing avast as the real Administrator account and an account of admin rights. avast install the same, works the same... I'm sure...
But, if you have more than one account with admin rights, oh, then you could have troubles with avast...