I used to be the person who opened and dealt with letters of this nature (disgruntled consumers wanting to make a point) in a previous jobs and while I can understand frustration and have no issues with swearing myself, such a letter would only have been read for humour purposes and then placed on file so there was a record of all transactions with the author, no action would have been taken despite the obvious frustrations. Yet if a well written letter with the same gusto and hatred came in without out the swearing it would be looked at and attempts made to rectify it, usually after the easy ones were solved by throwing a few free products to the customer.
So for the original question "Is this typical?" I'd say yes fairly typical but the author shouldn't expect an immediate or positive response from the person they are writing to.