Yep, it's all down to the calibration of the espresso machine. The grind, the dose, the pre-infuse, the pressure limiter and temperature control. Get someone who can't be bothered because they think it all just tastes the same and you get crap coffee.
The freshness of the beans is important, but chains have an advantage here as they burn through stock quickly.
The mix of beans affects the taste (obviously), but that is largely a matter of personal preference. I prefer the flavour of Arabica beans, but I don't mind the presence of Robusta in the mix. The chains tend to use mainly Robusta for their regular blends as it's cheap, but most offer speciality coffees (Costa's Old Paradise Street No 11 is an amazing single bean coffee).