The stuff coming out of Apple is really weird. They have announced that Leopard users can upgrade to Snow Leopard for $29. They have also announced that users who have purchased a new Mac since June 8 can upgrade to Snow Leopard for $9.95.
But they have been conspicuously silent about the intended upgrade path for Tiger users. Some have speculated that the intended upgrade path for such users is to separately purchase Leopard for $129 and the Snow Leopard upgrade for $29. However:
1) If this is in fact the intended upgrade path, Apple has not said so.
2) It would mean that Tiger users would have to pay $158 to bring their OS up to date, which is considerably more expensive than it has ever been in the past.
3) Historically, Apple stops selling 10.X when 10.(X+1) is released.
So while it is possible that "buy Leopard for $129 and Snow Leopard separately for an additional $29" is the intended upgrade path, it's quite a leap of logic to assume that it must be the case, considering that Apple has not said so and that it would inconsistent with past Apple practices.
All we can really say is that Apple is so far keeping Tiger users in the dark about what it will take for them to upgrade.
I suppose it's worth noting that we are talking about a relatively small number of users. Snow Leopard requires an Intel-based Mac. The first Intel-based Mac was the iMac Core Duo released on January 10, 2006. Leopard was released on October 26, 2007. So all we're talking about are people who bought Intel-based Macs during that 21-month period and have not since upgraded.