Been on the sales end trying to convert people before and I can tell you it isn't as black and white as that, although the analogy does stand up.
The issue is that although the basic product is the same, the brand, experience, etc are not and that is what makes the difference.
In terms of the utilities industry, this is a huge part to play. The old player has years of experience working in the industry and the new ones don't. They can offer the same product but when it comes to the provision of subsidiary services (customer service, billing, support, changeover), they are shockingly bad and that's where they fall down - sheer inexperience.
Back on topic, regardless of what people think of MS, IE is still a widely accepted brand and even with regular security issues, the brand and regular patching is a huge boost to IE's credibility with the masses. Hell, the average doesn't care about security vunerabilities or development issues - they do care about what they can use, what is easy to use, what they feel safe using - strong branding and regular patching goes a long way.
People view browsers as important facets of their PC's and most would rather trust the maintenance of these to MS over some random company they don't know (and perceived to be a lot smaller and as such less able to offer the same level of service).