Marketing guys? Sure, assuming you're in media or consumer web. You need your salespeople as close to the customer as possible. But why move your R&D to the US?
Developers wages in Israel are not even close to what a dev in the valley, or in NYC can make. Junior devs start out at 15K NIS/month ($4250) and the cream of the crop can make up to 30K NIS/month ($8500). Totaling to anything between $50K and $100K yearly. What does that get you in the valley?
Not only that, I would venture to say that finding the tech talent in Israel is easier. The mentality in the startup scene here is still not a cut-throat one. If you look hard enough, you can find the right devs you need.
Having said that, the startup scene in Israel still isn't as vibrant as you would think, at least when it comes to consumer web. The classic strengths of the Israeli tech scene have always been security, enterprise, IT and hardware. Consumer web? Google-scale? We're not there yet.