I don't agree with the idea that designers should just hand off mock-ups to developers and expect them to implement it properly. All of these points can be addressed by coding your own HTML, CSS, and Javascript. Developers don't have the time to worry about your grid, they have enough to do as it is. Design that stops at Photoshop is only half finished, and a web designer who doesn't have the skill to implement their work is not really a web designer at all.
When I work with developers, I just tell them to do their thing and make it work. Don't worry what it looks like - I'll do the rest. Using GitHub on our projects has made this really easy for me.