Most Muslims aren't Arab; "traditional dress" varies widely, even if it is actually worn. A lot of Muslim women I've worked with wear the same clothes as everyone else, without even a headscarf, and don't seem to have a problem coming to work on their own.
Certainly from surveys in the UK it would seem that the people who over-estimate the most actually live in areas where there is hardly any significant immigration, Muslim or otherwise. This is reflected by UKIP polling better in the areas with the least immigration than in those with the most, even though the latter in itself would not explain such a market difference in itself.