Well, it's really a matter of UI design. If we include add-ons at the time of buy-in, then rebuys would need to be included, too. While a bounty cost of $0 means no bounty chip is purchased, that isn't the case with buy-ins, add-ons, and rebuys (a player can buy-in, add-on, or rebuy for a cost of $0). So you couldn't just leave the add-on amount $0 while setting a buy-in cost of $40, for example, to indicate a player is buying-in but not adding on. There would have to be an additional indicator, like a checkbox. So now we're at
Name Buy-In Add-On Add-On Bounty
Amount
[ $40] [ ] [ $15] [ $5]
Jack Nimble [ ] [ ] [ ] [ ]
Jack Daniels [ ] [ ] [ ] [ ]
Jim Beam [ ] [ ] [ ] [ ]
Now we add Rebuys
Name Buy-In Add-On Add-On Rebuy Rebuy Bounty
Amount Amount
[ $40] [ ] [ $15] [ ] [ $15] [ $5]
Jack Nimble [ ] [ ] [ ] [ ] [ ] [ ]
Jack Daniels [ ] [ ] [ ] [ ] [ ] [ ]
Jim Beam [ ] [ ] [ ] [ ] [ ] [ ]
Don't forget that each of those actions (buying-in, adding-on, rebuying) have their own rakes.
Name Buy-In Buy-in Add-On Add-On Add-on Rebuy Rebuy Rebuy Bounty
Amount Rake Amount Rake Amount Rake
[ $40] [ ] [ ] [ $15] [ ] [ $5] [ $15] [ ] [ $5]
Jack Nimble [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
Jack Daniels [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
Jim Beam [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
And the user can define multiple rakes, which means we add those columns, or the rake amount becomes a button. And for each action, the player may receive a certain number of chips, and a certain amount of points (currently editable at the time of buy-in, rebuy, and add-on). As you can see, this has gotten a little out of hand now...
So, it becomes a complete mess, OR a new type of buy-in dialog is created for a specific purpose (yours, in this case), where only a few items are displayed. While I'm not against creating convenience functions, it should be beneficial to a decent sized audience to warrant the time and work involved.
So, what do YOU think?