Yes Talbot, I have to agree with Togo. This isn't just being picky. I've often found this. A lot of these units have a clear space at the top to allow for ventilation. A heavy, drop-down door causes the oven to tip forward dramatically if the top fixing screws aren't in place.
That's not the whole issue though. To answer Ferlew's question...
Under Law, every tradesman has a "duty of care". What Bright Spark is saying is that no visiting electrician will have an idea as to the safety of the existing installation.
In today's litigation-happy world, the electrician would be crazy not to carry out a few checks on the installed circuit. Any passing div might have installed that cooker circuit previously. All responsibility passes to the tradesman in these situations. He is certainly guilty of "covering himself", but he's of course covering your safety as well.
I don't want to be too po-faced about this. Many of these simply plug into a regular 13A socket these days, with four screws in the front mount.
All it is, is that when you call someone in, all responsibility is dumped onto them.
It's most likely a very simple job that you could do yourself quite easily.