The reason it's safe to use a full system or slip-ons with a stock map is the fact that your bike is already set to run a bit rich from the factory, and setup to read through the sensors to run a bit rich, which means it actually adds more fuel than what can burn. In VERY broad terms, this prevents the engine from basically destroying itself, because, the fuel helps cool/lubricate the motor. They do this for the same reason they make your speedo read 1-5% fast, they need to error on the cautious side. This is also one reason they install a PAIR system, or the SMOG system, it helps burn the unspent fuel before that "soot" can be blown out the exhaust, since it isn't running perfectly ideal.
There is an extreme science when it comes to tuning, I am by no means an expert but I spent a lot of time trying to educate myself on the basics to provide at least a decent tune on my previous bike running a Bazzaz with AFM. 14.7 AF ratio is the "Stoichiometric" ideal condition for burning fuel in a gasoline engine. Now with that said, each and every motor behaves different, and produces power different from one another. The way they are designed they produce similar, but that is why there is big money in blueprinting a motor and getting the most power out of it.
So with that said, if you increase air flow in, and air flow out, the ECU on the bike uses the two sensors on the bike to adjust fuel, and will increase it, or decrease it as needed an still shoot for a targeted AF ratio set by the manufacturer. This is where a good tuner comes in. They have separate sensors and read the AF from the exhaust, and they override the bike to get the most HP possible by adding or removing fuel.
So, you don't need an up-map for a full or a slip on... BUT, you DO need one if you want to improve performance of the bike to it's best potential. Sure adding an exhaust generally will add some peak performance, as it is a restriction point, and your bike's fuel map already compensates for the sensor readings, and increases fuel. But if you want the most HP possible, you need to get good reading to potentially add more fuel, or subtract fuel to get it ideal.
Again, general ideas, but that's why it doesn't matter. The up-map does other things, but it does change a bit of the fuel mapping to get it more ideal, but you won't burn up your bike with a new exhaust, but you might hear some more popping out of the exhaust as it can't deal with all the unburnt fuel it added, and most likely, you will get worse gas mileage.
