The Welsh one is right. It is first and foremost you who expects perfection, and as a result you appear to be flawless, or to aspire a state of flawlessness. Others notice it and are offended if you do make a mistake once in a while, because it makes you seem like an impostor. Clearly, nobody is perfect - however, people are too simple not to think in extremes. If you are a perfectionist, people will think that you are perfect, or that you think to be perfect. Any sign of imperfection will convey the impression that you are a pharisee, basically.
The truth is that people love it when others make mistakes. It makes them feel more comfortable around them.
This is just a consequence, though. People love similarity. Therefore, they love those who make mistakes - and dislike those who appear to be 'perfect'.
Really, all of this is a result of contrasting attributes. You cannot easily discern different shades of gray - however, it is easy to see a black spot on an otherwise perfectly white background. Since people are good at thinking in extremes, the polarity of life makes certain aspects of a personality, or a behavior, stand out. Such obvious aspects are then singled out by the observing people for further discussion. Moreover, people tend to think about you the way you think about yourself. If you want to be perfect, people want you to be perfect. Imperfection is therefore disappointing, since perfection was expected.