A PCMCIA is the laptop equivalent of the PCI board. So for the pc you have the 1820 PCI, the laptop has an 1820 build into the little PCMCIA Buscard. You've never seen it because there's hardly any other OEM's building pro pcmcia cards ( just RME really and they're costly compared to this, I gave them some specs here a while ago on their pcmcia cardbus which is basically the hammerfall ).
Why not firewire ?
Although the normal break box has firewire, it's still not clear to me if this is still the same with 1616. EMU does use firewire but not in the orderly fashion, meaning they haven't used it for the regular protocol. I doubt that the normal break out box is like the break out box on the 1616 because the features are 16 I/O's via Neutrik, with 48v phantom power ( but still with analog signal paths for clipping limiters, nice ... ), the 1820 has less analogue I/O as far as I can remember and no phantom support for all analogue I/O ( I thought it had 10 I/O's ).Considering that means they did a small overhaul of boards to make it compatible for use of laptop ( Im thinking about the little but unusual transformer on the 1212/1820, which probably is now placed somehow into the breakout box).
If it's better ? ....
Well, there been cases where Firewire had been used which created humm, noise of sort when used with laptop. I can't be sure about this but these are things I heard along other boards.
On the question whether the card is stable placed like that should be no problem, pcmcia cards are long and dont fall out their socket that easy. One pain though ( from experience ), if the plugs are shitty plastic and bends they're bound to break one way or another. I had this with a pcmcia modem, my girl made a stampede past the couch and ripped the cable the wrong way so the tip of the plug broke. There was no spare cable for this meaning I had to buy a new modem. It does look better on the 1616 being it a firewire plug, but it still needs caution.
Ow...the cardbus also works standalone, so you dont need the micro dock all the time.
Leaves one question.....
Can you still hook up the older break out boxes to this new cardbus ? That would be fuckin smart! 1212/1820 owner would only need the card bus in that case ( and a laptop ).