I think hardwork generally does lead to promotion up to a certain point. My company will allow you to go from a 1 to a 2 on good contributions alone and time. Going from 2 to Senior takes additional time, but is more than just technical. It's about how well you can train other members of the team, work on special projects of difficulty, work without direct guidance, give regular feedback to management, work across department barriers, deal with customers...etc. It also helps if you're persistent.
