Keeping Within Key

I understand the importance of keys in songs, so why is it nearly every song i find a tab for to play the chords has at least one chord, outside the key. Or does it not really matter too much?

Hmm, maybe those are results of artistic innovations ^^

What do you mean?

Artistic license. You're not limited to those chords, but those chords are the ones that "fit" best. Other chords tend to sound "outside", but sometimes that's a good thing.

Thanks "blackholesun" that was perfectly and simply explained.

artistic innovation.

nice vocab emp

err well, nvm... My skill at English language is not sooo good :P