Realism and verisimilitude are two completely different things.
You can make things unrealistic and maintain verisimilitude. When you break verisimilitude is when things get silly.
For example, in the golden age of comics, Superman might have been seen holding an entire building above his head. It's perfectly fine to assume that Superman had the strength to hold that much weight, but it's silly to think that the building would remain structurally intact when in essence all of its weight is being compressed down in two teeny, tiny points (Superman's hands). Superman's arm would simply punch through the building, not hold it up.
The difference between realism and versimilitude vis a vis gaming is that internal consistency within a genre is all you need as long as you are familiar with that genre. Like say, Toon if you have ever seen a Buggs Bunny cartoon in your life, which most people have.
Realism is the expectation of verisimilitude when you aren't already within a clearly defined Genre (Superhero, Star Wars, Vampires, Steampunk, Cthulhu, etc. etc.)
I think the problem a lot of people have with most FRPGs is that the presumed fantasy genre baseline can range from the fairly realistic low-fantasy world many people know from early fantasy novels, (the Conan books, Jack Vances Dying Earth, Fafhred and Grey Mouser) to the rather zany worlds of World of Warcraft, anime, or the throw-away Sci Fi channel movie of the week (Gargoyles vs. the SS or whatever).
In the former case you can bring your own expectations of everymans knowledge of the real world and history into, with the expectation that there will be a few fantasy elements (dragons, magic spells, potions whatever) but by and large the world is one you can expect to find your way around in. In the latter case, who knows whats going on.
Still worse, often, rather than being consistently in one zone or another, many FRPGs are a rather ill-defined and often confusing mish-mash of realistic and cartoonish elements.
G.