Question: I've started Wing Chun few days before. Everything seems to be nice, but I've seen some videos on internet, they say that Wing Chun can't handle Boxers or Wrestlers.

What are the comparisons between Wing Chun and boxing/wrestling that would lead someone to make this claim? Are there weaknesses that can be exploited?

Answer: 
As always, you can't compare style A with style B and say either one is better. It's not because you're a boxer, you immediately win agains a wing chun practitioner. It all depends on how good both fighters are, how much experience they got fighting opponents of different styles, the competition's rules (eg. if you pit a judoka vs. a taekwondo, and rules state no throws or groundwork, chances are the taekwondo will win. If the rules state throws and groundwork are allowed, but kicks to the head aren't, the tables will turn), and even as much as how good/bad a day someone's been having and even sheer luck (Remember, one lucky hit can be all it takes)

Of course, each style has its strengths and weaknesses. Once you understand your system well enough (and your own body, for that matter), you can start playing with the strengths and the weaknesses. You can get creative with them. That's an important part of the experience part mentioned above.

But yeah, in short: You can't just compare style A with style B. A kid who did 3 weeks boxing classes won't win against Ip Man. A kid who did Wing Chun for 3 weeks won't win against Mohammed Ali.
So there are some fundamental assumptions here that one must look at with "intent or goal".

**Goal:
To beat your opponent senseless?**

* If this is your goal then you will probably want a style that focuses aggression and subjugation of your opponent over anything else.

**Goal:
To protect oneself?**

* If this is the goal then any discipline which focuses on body mechanics as well as properly analyzing a situation and working to diffuse it works well.

**Goal:
To develop oneself through discipline and mastery of ones body?**

* If this is the goal then the ability to "beat someone" isn't really as important as the type of person you become through the exercise and mastery of the art. Boxing, Wrestling, Kung Fu, Tai Chi, Karate, etc... all have the ability to develop ones physical and mental techniques while disciplining and harnessing ones own inner self for personal growth.

P.S. Unless you are practicing just for a MMA full contact event, then any style has use, purpose, and value. The only caveat to add is if you are grappling it's hard to hit and if you are at a distance it's hard to grapple, so there is a body mechanics balance needed to be well rounded.

P.P.S. As far as ability to beat another opponent, this is largely circumspect on the individual's abilities and if one is better skilled and physically capable then they will likely win regardless of the style in question.