This sounds interesting, but to clarify...
Let's say that we had three people join. One put in 5, one did 10, one did 15.
The person who put 15 would win the 50% of all (or 15, oddly enough)
The person who put in 5 would get 49% (or 14.xx)
The person who put in 10 would get 0, since they put in the "average" amount (5+10+15=30/3=10)
Is that correct?
Yep, thats correct
The only thing, thats happening additionally is that stakes which are virtually zero are being filtered out. The current threshold for this is 1% of the average bet. If a stake is lower than that threshold, it is simply being refunded (if it was bigger than the transaction fee, at least).
If these stakes would be allowed, staking a few satoshis would be an almost guaranteed winning with no risk..