Aiden's got it right - there is huge benefit in a new interface becoming ubiquitous across all platforms, including existing (vs new only) desktops. Allowing TBolt expansions to do PCIE only would be a huge benefit to consumers, as well as those pushing the standard, as let's face it, USB3 has a headstart. There's no reason USB3 and TB can't co-exist...for a time, but let's look at firewire and USB2 - fw is much superior not only in speed/bandwidth but also technically (target mode, fw based networking, etc.), but what happened? Too expensive relative to USB2, didn't get pushed for *every* system possible - do we see any overlap with TB yet? Make it 'free' or nearly so for as many devices as possible, even if it's without displayport for existing systems. Delaying or putting barriers to mass deployment and use just means it takes longer, or becomes niche only as everyone moves to more available (on their system) USB3. Apple ignoring USB3 in their systems doesn't mean the world waits for them.
Chaining of devices is an obvious win for anyone in the pro category - guys doing HD video editing even at the amateur level need storage, and fast - of course they're going to want a fast RAID array. Want to add another device? Video cameras, mixers, anything? Plug it into the end of your array, or display. A single connector to 'rule them all' along with daisy chaining simplifies cabling, simplifies re-use across multiple systems and allows investment in some/many cases that isn't thrown out on the next system upgrade/replacement, and as long as each device plugged in supplies at least out daisychain port, no more forgetting to bring a USB hub or running out of the lame 1-3 USB ports on a laptop with 5 devices, etc. Very convenient. Also, GigE saturates in the ~100MB/second range as stated, with current drives (let alone SSDs) able to saturate it, and you really do NOT want to try pricing 10GBe switches for home or 'small professional' use.
Take another step, and Apple *could* make a single TB port into a universal interface, beyond external bricks. While that alone is pretty exciting if someone does it reasonably well to include graphics, USB3, and daisy-chain ports, what about iPad 3, along with the rest of the the laptop lineup? Universal single docking station. Drop your iPad 3 (or maybe Android tablet in the future, if Intel plays nicely and cheaply enough), MB Air, MBP, and ideally, any other laptop in place, one plug and there you go - desktop graphics, daisy chain ports for TB, any additional storage and other devices, a few USB3 ports, optical drive (optional, plugs into the chassis), keyboard etc - all available, all the same across all devices you plug into it. iPad 3+ now becomes a feasible mobile note taking device, and psuedo-desktop using external storage, reasonable graphics, etc. MBA becomes a lot closer to MBP-capable when plugged in (storage, video, expansion slots), MBP becomes easily able to be made thinner without losing too much except for optical drive.
Check out the growing number of tablets adding keyboards, or more closely, the vaio Z series Power Media dock - their 'dock' attached to a 13" ultralight adds a discrete 1GB RAM GPU, USB ports, and can drive up to 4 displays. The most amusing part? They implemented LightPeak over a USB3 port and that's their dock connector.
There are lot's of great possibilities here, the question is how far it will go, if Intel will help with adoption or if it becomes a failure vs USB3, how greedy companies will get on pricing of TBolt expansion chassis/devices, etc.
