It sounds like you immediately toss the query if it doesn't follow the described format.
I don't, actually. If you wrote a complete novel, took the time to write up a query letter to a professional literary agency, and paid for the postage, I feel soundly that the whole letter should be read. (Plus, it doesn't take me a long time to read a 1 page letter)
If you have a sound manuscript and are capable of conveying that somewhere in the letter, I'm willing to forgive a few spelling, grammatical, or formatting errors. Nobody's perfect, or maybe the author didn't really do much research on how to write a query letter and spent more time focusing on perfecting their novel - a better idea in the long run. Or, there's the occasional abomindable query letter with excellent credentials that just goes into the maybe pile immediately. ("I won the Booker Prize for Short Fiction, had my previous book turned into a movie, and my previous agent was at William Morris but died recently and I need a new one.")
My job is to sniff out quality material. Sometimes the query letter isn't perfect but the concept is interesting enough for me to pass it on and my boss to request it. However, it's best to give yourself every possible advantage by polishing your query letter, because many agencies will NOT give you the time of day if you even call your manuscript a "fiction novel." Many assistants and agents are looking for a reason to reject and will take any. In short, try not to screw up, but if you have a great book, you will probably get some offers even if there's a spelling mistake somewhere.
If the format is followed, what part of the letter convices you to put it in the maybe pile?
I get this question a lot, and the answer is always, "It sounds like a really good book." Since there's no one right way to write a great book, I can't really tell you that way. I can only tell you the wrong way to present it. Sorry.