Statistics is a strange science. Percentage of return visitors doesn't mean much unless you compare it to the number of visitors. If your traffic is increasing, the displayed % of returning visitors will be lower than it really is. If your traffic is declining, the displayed % of returning visits will be higher than it really is. The % is accurate only if the traffic is steady.
The different results seen in this thread could also depend on the amount of time that needs to elapse between pageloads for a pageload to be considered part of a new visit. I think Google Analytics stores the cookie permanently (until the user deletes cookies) though. But other counters may have different rules, so if you're using one, check on that.
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