Easyjet aren't the only airline to do this. Remember that all the money at the end of the day doesn't go directly to Easyjet but to the catering company and quite often it is they who make the stipulations. It is all to do with what denominations can be banked and what can't. As a direct consequence, on flights operated by continental crews (i.e ORY, CDG, MAD, GVA, BSL, SXF etc etc) all coins are accepted.