Not really a good comparison here, the Citaro is a complete bus
product where the general look of the bus remains largely the same
across all customers, the C1 facelift Citaro has been around since
2005, For the Citaro, you either choose the C1 facelift or the C2,
not much choices here.
On the other hand, the A22 is a chassis product which allows
customers to fit their body of choice, ultimately this means the
customers have a lot more choices in how their buses will look. If
a customer wants an older front for parts commonality, then its
their choice. If however the customer wants a new front or an
entirely different body manufacturer, they could do so, and the end
product will be a different looking bus.
Well you could get a Citaro C2 in Euro V (in fact, the only
option for Singapore):
http://www.mercedes-benz.com.sg/content/singapore/mpc/mpc_singapore_website/enng/home_mpc/bus/home/new_buses/models/regular_service_busses/_Citaro_c2/facts/technical_data.html
So does it really matter if it's C2 or not? I can't blame the
lobbyists for digging its looks (just as you would stare at a hot
lady), but I think SBS Transit knew what it wanted when it chose
the older option.