rotation - Would an exoplanet without axial tilt have no seasons?

I considered this as an explanation for George R. R. Martin's books, where several years could go by during each season. If the planet had no axial tilt and very little eccentricity in its orbit, there would be no annual seasons. But if solar energy output would vary sufficiently, you could have seasons, with inconsistent cycle times that measured in decades.

So I thought, "Ha, it is possible."

Then some character in the book noticed "the days were getting shorter" and I had to throw it out. In such a world, day length would always be the same, and it would always match night length.