it's been vs it has been

Some examples from the web:

• May 14, 2015 ... To my knowledge, the 2nd one should be grammatically correct but often hear the 1st one "It's been a while since I've ~". Which one do you ...
• So far as I know, this is the first time as here you've been, since it's been known as the bailiff's in the house; and I was here yesterday, and looked at all Bessy's ...
• "It's Been Awhile" is a power ballad by alternative metal band Staind. It was released in March 2001 as the lead single from their album, Break the Cycle.
• May 17, 2008 ... And it's been awhile. Since I've gone and fucked things up. Just like I always do. And it's been awhile. But all that shit seems to disappear

Some examples from the web:

• I must know that it has been consummated.
• I have kept your secret, and it has been really tough.
• Although this vessel is Cardassian in design, it has been appropriated by the Maquis.
• Your life as it has been is over.
• Do not use Aranesp if you think it has been frozen.
• It was very successful and it has been a pleasure working with the presidency.
• But it has been a useful debate which has reflected the importance of the subject.
• Finally, it has been established that this phenomenon is often closely linked to organised crime.
• Yes, it has been a pleasure.
• Ben, it has been an honor watching you work today.
• Moreover, this system functions excellently where it has been introduced.
• I know that it has been very difficult to bring this very important Directive to fruition.
• Don't worry... it has been worse for me.
• Mr President, it has been a long hard road on this directive.
• When they have asserted themselves, it has been largely in pursuit of narrow national interests.
• This is always the way it has been.
• The current Directive includes such a provision but it has been excluded from the proposed Regulation.
• We worked together, Parliament approved it and it has been accepted.
• So far it has been an exciting year.
• Since then, it has been refuted both by political experience and statistical testing.