Why are you offended? The market considers them senior...
In 2 years of experience how many serious products can you take from start to finish? In my opinion, a senior developer is a person who did this multiple times.
It's almost like calling yourself lead developer of 1 man team...
Titles merely offer a bracket of salary that a resource can have, once they reach the peak they either have to go up a rank or leave to get more pay.
Except the responsibility of leading other people, on a resume this title would imply you gained that experience while in fact you didn't.
Note that I didn't say manage other people. I'm talking about helping get the better of the team, showing a junior member how things can be done better, etc. Like a team captain, not a coach.