Question: I playing guitar since a couple of years (but not regularly) and I always wondered if guitarist from known bands always play their songs/solos perfectly?
Especially when the songs are fast paced, is it easier to make mistakes that no one will notice? When I play solos I am never really satisfied with my performance since it doesn't sound exactly the same like in the song.

I know there is no exact answer but I would like to know what you think so I can silence my conscience :)

Answer: 
'Perfectly': never. 'Very Good': usually. Professionals tend to want to show you what they can do, rather than what they can't; it's their meal ticket, after all.

One of the skills in being an instrumentalist though is to practice techniques that allow you *to* power through small mistakes without disrupting the rhythm or the overall feel of the song, or letting your small mistake trip you up and turn into a bigger one. Pros will generally be good at this aspect of instrumentalism too; it's one reason you may not notice their mistakes.
I'll talk about live performances since, as other posters have mentioned, recorded performances can easily be fixed with editing.

Mistakes? Yes. Always.

But don't let them stop you!

As a not-top-notch performer I can tell you that there is a stark difference between your (the performer's) perception of the performance and the audience's. In a band situation, you are concentrating very specifically on what you are playing while the audience is taking in the entire performance of all of the members. Not only are you paying more attention to your own performance, but often there are monitors allowing you to hear your performance more than that of your bandmates. This can make you think "wow, that stood out like a sore thumb", when really it's not as prominent as you are hearing. 

Further, you can feel your mistakes. You feel your fingers slip or not hit the strings with enough force. This extra sense of the mistake underscores when they happen. 

An interesting aspect is that due to the nervousness of playing in public and having practiced a song many times, you are perceiving time differently. A mess-up will feel like it lasts an eternity but typically they are over so fast that it will fly by before anyone gets a chance to notice.

The real key to a good performance: when you inevitably make mistakes, don't let it show. Don't make "I messed up" face. And after a performance, just don't mention mistakes, even though it might be the first thing on your mind.