As others have already pointed out, the reasons for having a crossmatch performed every time prior to a transfusion is for 2 principal reasons; To ensure that the blood allocated from inventory is ABO compatible, since an ABO incompatibility can have serious, even fatal outcomes, and secondly to check for the appearance of any unexpected antibodies within the circulation that may have developed from exposure to foreign antigens in previous transfusions.
The development of such antibodies is not guaranteed, but if they are present, they can again cause potentially quite serious medical complications - not something you would want at any age, but especially when you are 80 odd :)
Steweys description of what happens during catastophic blood loss is quite true, but slightly out of date now in that, in situations of catastrophic blood loss the initial concern relates to getting fluid into the patient to maintain blood pressure and prevent the patient going into hypovolaemic shock. This gives time to group and cross-match blood for the patient.
I have been involved in situations though where the ongoing management of a patient with multiple injuries has meant the transfusion of over 100 units of blood after the initial treatment with IV fluids, and in those situations we do not bother with a cross match; We only ensure ABO group compatibility, and in extreme cases it is not unknown to switch to different ABO groups in an effort to keep up with the blood loss.
Thankfully though, we new developments in IV fluids, peri-operative blood salvage systems and advances in treatments, such situations have become very rare.