Simple script

Hello , 

I'm wondering why when I try to run loop script it doesn't work . For example when I run 

get-wmiobject -computername comp1 win32_startupcommand     - it works 

but when i try something like this :

$comps=get-adcomputer filter * 

foreach ($comp in $comps) {

get-wmiobject -computername $comp wmi32_startupcommand 

}

it doesnt work ... 

any sugesstions ?