Why or why not? As a corollary, I saw a presentation description in a recent CCC demonstrating the (non-hostile) use of micro SD cards as a cheap source of processing power. Does this render micro SD card fundamentally vulnerable, or potentially vulnerable, to the same type of attacks? Why or why not? Does it make them open to other forms of attacks? Why or why not? Are there other alternatives that are immune? Micro SD cards are nice because there are now SD card bays in most mobiles and workstations alike.
SD cards of any flavour do not provide processing capabilities except internally to support standardised data access. They are not a source of processing power, cheap or otherwise.
The main advantage over a USB key is that it is harder to squeeze the required hardware in them that could be used to attack a PC via the USB port. That does mean they are less vulnerable. Also, the standard interface for SD cannot be used for power which removes some of the other potential issues with a USB interface.
There are cards that do have processing capability and that have the same connector layout as SD cards, Smartcards and SIM cards for example. And there are smartcards that have significant security processing capability (most have fairly minimal capabilities) but this is not the same as the SD memory card format.
So bottom line is that SD card slots are safer than full USB ports but they are not immune to some attacks such as autoplay.
If you need more, look for a PC with a smartcard interface.