It doesn't work like that, unfortunately. What you seem to have forgotten is all the time that has passed since Leopard was released. That is quite some time that all the Tiger users have not been able to benefit (if that is the right word) from the use of Leopard and still they are expected to pay the same amount in total to upgrade to Snow Leopard as someone who had bought Leopard in the first place.
If you don't need/want iLife or iWork, it is a waste of DVD and packaging.
Your logic is twisted. Tiger users have had every opportunity to use Leopard since the day Leopard shipped if there machine was compatible, and THEY upgraded. Upgrading is an end-user choice, and one has to assume current Tiger users did not to so because they were happy with that OS or their hardware did not support Leopard. Thus, to argue Tiger users have "lost opportunity," is nonsense.
So again, I'll state, what seems to be obvious to me if you do the math. The entry cost to 10.6 is materially identical regardless if you are a Leopard user paying for the $29 upgrade or a Tiger user paying $160 for the box set. The difference being, Tiger users will have to pony up the entire $160 all at once where Leopard users already paid-in there $129 and now just pay another $29.
If you look at how most other companies approach upgrades typically users that chose to skip a version have to pay MORE, not the same, or less than more current version users. Would you make the same argument to an owner of Photoshop 7 who wanted to upgrade to CS4; i.e., The upgrade should cost the PS7 owner less because he has not had the benefit of CS, CS2, or CS3?
Again, Tiger users get the better deal here with the added bargain of the two software suites that most everyone else had to pay extra for if they wanted them. If you don't want iLife or iWork software then sell it or give it away to someone that can use it -- you know, recycle it. But bottom line is you are not paying more for 10.6 than the $29 upgraders.