Absolutely. In a similar vein, have you noticed, the reviews with "Amazon Vine" next to them are typically full of platitudes & praise?
I appreciate Amazon's transparency, in fact I applaud it, but I think the whole Vine program is a bit brain-dead ("Hey we just shipped you a brand-new 60" Samsung HDTV, please let us know if you like it.")
IMO the Vine reviewers would have a lot more credibility if reviewers had to return the product after 30 days (shipping paid for by Amazon). I'll bet if you check most Vine reviews, they are made within 7 days of receiving the product, and I bet they average something like 4.5 stars.
If there is a big-data person from Amazon reading this, try instituting a 30-day "use & return" policy for Vine, and watch participation go down, along with average review. That will tell you who's in it for free stuff, and who's actually interested in using products & writing meaningful reviews (don't get me wrong, I'm not one of them, I wouldn't do it...)
Even though Vine "membership" isn't tied to the average review you give, and (in theory) the terms of participation in Vine are such that Amazon can ask for any Vine item to be returned to Amazon at any time, that's not the reality.