I would tend to agree with this, on about four points that come to the top of mind (though I am not a commercial producer of either, I observe what my friends and neighbors in the business experience):
1) Grapes have more bug problems
2) Grapes have more potential frost problems
3) With grapes, you have to watch your sugar contents really closely. With hops, you grow, you harvest, and often you turn into a dried pellet form, IE: the end-product with grapes is more temperamental.
4) You are (typically) aging wine longer than beer, so there's more time when something can go wrong. Had a friend who was cellar master at a winery. New guy comes in and does something stupid, ruined wine that had been sitting in barrels for two years.
Regarding 3: the same goes for beer, except you can mess up over the course of just a few minutes to an hour instead of a few months. Crush your malt too fine or too coarse, mess up the mash temperatures, and you end with things like a too high or low efficiency, a stuck sparge, or too many fermentable and unfermentable sugars. Of course, in a fully automated industrial brewery this usually isn't a problem, but your typical nano or micro-brewery is a still a lot of manual works, and thus many ways to mess up manually.
Edit: and now that I think about the other things:
Regarding 1 and 2: some hop varities have mildew problems, and bad weather has negative influence on the growth and other things like alpha acid, so bad weather can have quite the impact on hop quality and availability. The 2013 hop harvest in Germany was quite the disaster, apparently. AA% is a lot lower, and young plants of some new breeds got way too much water.
