A bit of hijacking but just to clarify things. You are right when you say about different widths. Manufacturers fit different widths to loads of cars, Audi fits wider tyres at the front to tune out understeer (not that they managed to), the rwds have wider at the back, lotus even fits one inch bigger wheels at the back etc. However I was only talking about the compound, the type of the tyre has to be the same. Tyres behave differently under different conditions, some are better in the wet than others, some are grippier than others, some need more effort to reach the optimum temperature than others...so many different things to take into account.
For instance, you can't fit contis at the front when you know that these tyres are extremely grippy when cold and 070s at the back. At the first lift off you would be heading straight in the ditch. Similarly, you can't do the other way around either, the car would understeer like mad. You can't fit a tyre which is great in the wet on one axis and an inferior one at the rear for the same reasons. Different compounds mean different grip levels at all temperature range and conditions, if you have more grip at the front then the car will oversteer and vice versa. My point is, if you value the handling of your car you should fit same tyres all around.
By no means this is a dig or something, all comments are well-intentioned and I'm not saying that that was the reason the OP lost control of his vehicle. The above mentioned effects can also be had when same tyres are worn differently of course.