Haha, right when I read this comment, Software Update alerted me that there's a new "Migration and CD/DVD Sharing Update" for download:
Wonder what that's about...

You can't power anything over eSATA, unlike USB or Firewire. Also, you can't daisy-chain devices like Firewire. The max cable length for eSATA is only around 1 meter, before the signal deteriorates, where FW800 is around 100m, and USB2 is around 5m.

Time Capsule. (In Apple's dreams.)

That's right. The question of "how do I migrate without FireWire" was answered with the original release of the MacBook Air, which already had no FireWire port. Back then Apple enabled migration over Ethernet, including wireless. If you do this, wireless is sure to be much, much slower than Gigabit Ethernet.

Because Apple already solved it back then, high-speed migration...faster than FireWire 800, if you use Gigabit Ethernet...is not an issue for the new MacBook.

I don't even use Target Disk Mode that much anymore, if I just want to transfer files fast, Gigabit Ethernet is both faster and easier. While all my Macs support TDM I only use it if I couldn't fix a problem over the network or with AppleJack.

That said, while all that's technically true, I personally do find lack of FireWire a deal breaker on the new MacBook.

The MacBook still has integrated graphics.

I wouldn't be surprised if the MacBook's lack of FireWire works out just like the original MBP's lack of FW800. Customer demand brought it back.

Alternately, Apple may be phasing out FW400 in anticipation of FW1600 and/or FW3200.

So? You put a separate power cord in the mains. No problem.
I’ve daisy-chained two Firewire disks (although they both don’t always come up on the desktop).

Yeah, other posters have mentioned that. Makes no sense to me. You remove FW400 when you’re ready to roll out FW1600/3200 connection -- not before. I find transfer rates to external USB disks so intolerably slow that I simply gave mine away!

Technically, the graphics chip is still integrated, but has been upgraded from Intel's chip to Nvidia's chip.

I agree. On the other hand, it doesn't make any sense to drop FW400 and retain USB 2.0. FW is noticeably faster. Apple might be trying to further distinguish the MacBook from the MBP (a possibility previously mentioned, I think), since they are aesthetically very similar now. It also pressures some MacBook users into buying the MBP when they upgrade.

Personally, the lack of FW400 is a deal breaker for me on the MacBook. I was going to get a new MacBook and sell my current one, but now I'm either going to keep my current machine a while longer, or get an MBP. Or, less likely, get an iMac.