"I don't know this stuff" is probably valid for many but saying "I don't know this stuff because I am woman" is silly.
But at times you have to keep in mind that still in many of the households girls are raised that way- they are simply never tought to deal with technical stuff and are used to see men doing it. They are afraid that they will damage something instead of fixing it. Some jobs may really be physically demanding which they really cannot do well. Some may know how still may not want to chip their nails and spoil the manicure.
The women who drive buses and taxis are trained for the job first. As for men- yeah- but then those guys talk about cars. lol.. they hear terms and are often more aware of the parts. It's not like a guy who has no idea about machine would suddenly figure out something a woman can't under similar conditions. I have seen such guys who didn't. ONe of them offered to start my bike which wouldn't start by simple kick one day. He tried to do it with lots of enthuasism but without pressing the clutch.
I have an Uncle. I will shoot myself before asking his help for any techinical know how. His wife, my aunt is the one I would go.
The main difference often is that a woman may bluntly say that she doesn't know if she is in doubt. Men try to deny if they are lost a road by miles.