As to the benefit for manufacturers, I'd say that it always is a market benefit to assuredly say that you can work with more partners. That means you aren't excluded from a job because a customer wants Company A in the spec when you only work with products from Company B. If your systems are talking to all of these solutions, moving data seamlessly, you stand to gain more business.
Drinking the standards Kool Aid, I think is one of the best things our industry can do. And whether you drink the grape or the cherry flavored Kool Aid (or even if you drink from the cups of both PSIA and ONVIF), it really doesn't matter. The fact is that specifications/standards development efforts are a sign that our industry is starting to mature beyond being a technology Wild West. Eventually every industry moves away from being a fragmented proprietary industry by adopting real standards or de facto specifications and it's wonderful to see this change happen today.