A gas appliance burns fossil fuel and produces exhaust gases which (in grills and oven) swirl around and infuse the food and thus, one presumes, affect the flavour. The food so affected is ingested with whatever effects swallowing a cocktail of added compounds have on the digestive tract. While production of electricity in the UK pushes the same "added ingredients" into the atmosphere which the population then ingests through the lungs, electric ovens and grills add nothing to the food other than heat.
Smoking affects the sense of taste and maybe some like that too.