New York deli sandwiches are certainly not representative of what you get everywhere in the US. They are famously large.
They may be famously large, but I don't think they are abnormally large for most of the US nowadays? I certainly didn't think they were particularly big when I visited.
And expensive to match the size! A pastrami sandwich at Katz's is ~$30. A croque madame at a similar place in Paris is ~€15.
People generally split a Pastrami sandwich over a couple meals or with someone else.