I get the sense from a recent email
My suggestion: Make very sure the client has that sense. You may just shoot yourself in the wallet.
It is quite possible the contact is harried, boss is on their back, and they just fired off an email without the time to consider how a terse wording or turn of phrase comes across.
That said, if this is a recurring problem with a number of clients, it's possible you're communicating something in a way which positions yourself in their mind in that way. This is not an unheard of attitude when the service or product is a commodity.
Watch how a pizza delivery guy is treated. Watch how a maitre d' at a fine restaurant is treated. Watch how both interact with the customer, the context of the interaction. Can both be ill treated by their clientele? Sure, but what I am talking about puts a degree of control in your hands.
People don't collaborate with hirelings, they dictate to them. People collaborate with experts. They are two different roles, each has behavioral cues, and you don't get treated like an expert should your perception be the "web site delivery guy."
My apologies to the web dev/design community, but the difference between these two roles is not as simple as a paper thin Web 2.0 aesthetic veneer.
A single instance does not a pattern make. Yet, it is not entirely beyond the realm of possibility you're putting something out there clients (Plural) pick up on.