Yes the price for upgrading to SL is higher for Tiger users, but my guess is that many Tiger users are also on machines with PowerPC chips and aren't even eligible to upgrade anyway. However, once some of these people find this out, there may be a halo effect on Leopard (10.5) which spurs these people to go out an get that OS knowing that it's the end of the upgrade path for them.
As for price and margins, SL has always been a tricky sell because the average consumer is UI focused and really doesn't care, know or care to know what's under the proverbial hood. Many people buy the machines because of looks - shallow, I know. OS 10.6 in a nut shell is designed to get more juice for the squeeze when it comes to existing hardware as well as position Apple to do the same for future hardware generations. From an eye candy POV, SL doesn't really deliver (and that's not what it was designed to do) and that's precisely why it's $29.
On a future note, I can't see Apple giving the same treatment to OS 10.7. I think that release will be much more end-user focused. What will be neat will be in 18-24 months when Apple it unveils 10.7 and says, "In 2009 we gave you Grand Central and OpenCL. We've been hard at work utilizing those technologies ourselves and this is what their power can do...Behold, we give you 10.7!"
