However in this case with Ebay it wasn't a stock split but rather a big chunk of Ebay (Paypal) split off into a separate independent company. I think what happened is when Ebay and Paypal separated Ebay share owners gained the equivalent Paypal shares. So this would throw off the numbers.
Can you explain how stock splits are accounted for in the "Percent gain" calculation for this case?: http://newinvestordaily.com/what-would-it-be-worth/r/30991
Intuitively that value would be much larger (300% or so instead of 40%).