From my perspective, games usually have both a tone and a milieu. A universal game or a house system will usually maintain its tone even when applied to different milieus. For example, Savage Worlds is a highly pulpy game. You can use it for pulp western, pulp horror, pulp fantasy, or pulp sci-fi, but it will always be pulp. Similarly, GURPS is an attempt at making a game that simulates reality – sometimes reality with some exceptions, but it tries to be realistic. Any game run in GURPS will be "realistic" – sure, there are modifications you can make to the rules to reduce realism, but even with those in place, that's still the baseline.
So, there's a limit to the kind of things you can reasonably do, even with a universal/house system. And trying to go outside it will usually feel odd – you can make superhero characters in GURPS, but the game won't feel like a comic book as long as you have one-second turns and detailed hit locations.
So, there's a limit to the kind of things you can reasonably do, even with a universal/house system. And trying to go outside it will usually feel odd – you can make superhero characters in GURPS, but the game won't feel like a comic book as long as you have one-second turns and detailed hit locations.