Useless Isnull() for formula

That's right, or to be gentler, next to useless in Salesforce.com formula.  Let's recount:

• Can't be used for TEXT, Rich Text: use Len()=0 instead
• Can't be used for Address: use AddrFieldName=''
• Can't be used for lookup (ID) fields: use isblank() instead - I just realized it today
  
• Can't be used for pick list: use ='' as well

That's a large chunk of things you may want to check for null condition...  Why couldn't they have a more flexible, "overloaded" isnull()?