In general there is some truth to what they claim is the difference. It's supposed to be about how complex the work is. Senior devs should be dealing with more architecture/design, more coordinating with other groups/teams, and have greater expertise (they measure this by output and opinions).
If you get promoted they expect more output and hours. The policy is 7.5 hours per day but they unofficially expect 8.5 hours for senior devs and tech leads. It's a 15% jump in hours and only a 7% raise. I've actually filled the role of tech lead and then senior dev for two years on a previous team. They never officially promoted me due to politics and wanting me to work more hours than policy states. I've been passed over and screwed over probably 4 out of my 8 years here.
I'm an intermediate developer and have been at my company 8 years. I've been told by managers whom I am personal friends with that if I stay at this level much longer (5 years now), then the company might look for a reason to get rid of me.