First of all, those prices ($62.64 and $37.89) do not appear anywhere in the current USPS pricing charts. Where did you get them? Here's a link to the official USPS rates publication, Notice 123.
http://pe.usps.com/cpim/ftp/manuals/dmm300/notice123.pdf
USPS has two size thresholds for Retail Ground and Parcel Select Ground: Package with a length-plus-girth over 84 inches (but not over 108 inches) ship at the "balloon rate" which is the same as the price for 20 pounds, unless of course the actual package weight is greater. If the package was just a little bit smaller (i..e, L+G of 84 or less instead of 88 inches) it would ship at the weight-based rate.
The length-plus-girth of your first package is 28 + (19 + 11 + 19 + 11) = 28 + 60 = 88 inches. It will ship at the 20-pound rate even though the actual weight is less.
The second package has a length-plus-girth of 17 + (14 + 13 + 14 + 13) = 71 inches, so it is not considered a "large" package and it will ship at the weight-based rate. The postage cost for a 9-pound package via Retail Ground ranges from $8.72 - $33.75 depending on distance.
