Hasn't all the software that was in the package been replaced with newer versions that now sell for less on the Mac Store?
They certainly would not put Snow Leopard in the Mac App Store, mainly because of Lion. Of course, for software such as iLife and iWork, that would be going into the Mac App Store, which has already been done.
So, at this point, does this mean that anyone wishing to upgrade from Tiger to Snow Leopard just needs to buy the DVD that's on the online store? On the Apple website they state:
To upgrade your Mac to OS X Lion, you must be running OS X Snow Leopard. If you have OS X v10.5 or earlier, purchase Snow Leopard now and install it on your Mac. Then buy OS X Lion as a digital download from the Mac App Store
Does this mean they no longer consider it breaking the software agreement to use the DVD and not the boxed set to upgrade from Tiger to Snow Leopard?
I don't think they ever really cared too much which version you were using to do the upgrade as from a technical standpoint either one has always worked fine. I would point out that if you are only upgrading to SL to be able to upgrade to lion the USB installer should work just as well for you in only one upgrade instead of two. The only reason sl is a requirement to upgrade to lion is that it is distributed through the app store which requires sl, if you get the USB installer (or make ur own) it'll install just fine assuming you meet the minimum hardware requirements (which would be the bigger concern if the machine originally shipped with tiger).