I'm liking weasels suggestion, where you could have "max kills" on a mob before it pops. I'm not so sure about making those kills belong to one player, but just force it to pop for who ever kills it when max kills is reached. Obviously reset back to zero when it does pop.
Using random numbers to determine whether an item pops gets mathematically flawed the higher the numbers get. Although mathematically speaking the item given a pop rate of 1/50 should pop 1/50 THAT IS ONLY ON AVERAGE... and the max time it takes to pop could actually end up being in the 100's of cycles.
I made this quick Sub in Visual Basic...
Private Sub TruePopRate()
Dim intCount as Integer
Dim intValue As Integer
Dim blnFound As Boolean
Do While blnFound = False
intValue = Int((50 * Rnd) + 1)
If intValue = 50 Then
blnFound = True
Else
intCount = intCount + 1
End If
Loop
MsgBox "You killed the mob " & intCount & " times for pop."
End Sub
This Sub set the poprate as 1/50, but you can see for yourself, sometimes it can mean you have to kill into the 100's (178) was my highest, in order to get pop.
Max kills could be 1.5 or 2 times the poprate.
It's an absolute no brainer that most 5x40's that have squandered there lives playing this game for an excessive period of time, won't like this idea under the typical... "My Life is Hard, I'm gonna make yours to!" rule... I already know your opinion... With less players on... and an ever increasingly sized world, there are less items around to be traded as spare, like maybe there was in the past. (Or maybe Brad's alts have them all

)