Yeah - I'm sure there's some of that as well. I think its mostly just 'design by committee' for the most part though. A lot of companies don't do sponsorships, etc. so they don't really need to worry about it.
As others have mentioned, it can also be tailoring a position for a specific candidate just so they have a reason to hire the person they already selected.
The rest are usually added by various levels of management that feel they need to 'contribute' something.
However, it makes it a PITA to get past all the databases/HR/etc. to actually get to someone that knows the 'real' requirements