Vague phrases may have carelessness or courtesy at their source. But vagueness resulting from unnecessary jargon irritates your audience. Why do people lapse into jargon when a simple, clear statement would communicate the message just as well? Some use jargon to impress; others use it out of ignorance, unaware that others don't know what they mean; some use it to hedge or cover up for having nothing to say.
Of course, you need to use the jargon of your profession on occasion. Words such as turnkey contract, footage contract, or daywork contract may substitute for more than a sentence or two of explanation.
Chemists, physicians, accountants, lawyers, teachers, gymnasts, customer-service representatives, plumbers--all have vocational jargon useful for expressing complicated ideas to their colleagues. But the key to jargon usage is knowing when to use it and when to avoid it.
People from other departments of your organization, managers removed from the specific workings of your division, and clients expect the same--simple, clear words, relevant and meaningful to them.
If you don't say what you mean, don't be surprised or angry that you don't get what you want.