It's not just about how much weight the stand can hold. How well-balanced is it? How well-balanced is it while being raised or lowered by hand? Keyboards are typically fairly even in terms of weight distribution, and have a low center of gravity. Monitors, not so much.
One would hope... 88-key keyboards are 45lbs (about twice a normal 27" monitor) and the older ones are significantly heavier... a non-POS stand should take >120lbs without a hitch.
That being said, there's certainly nothing wrong with a product better tailored for its purpose.