In new devices with SD card slots...

[japlytic]

...I typically expect them to support SDXC cards, but that is not always the case.
It has been about three years since the SDXC specification has been finalized, and there are still new devices (even new models) which do not support SDXC cards.

[mariushm]

Not needed.

SDHC supports up to 32 GB - most devices don't really need more than this in a very portable way.

So SDXC means simply more licensing costs ... you pay Microsoft for the exFAT file system (while you don't HAVE to use it, most customers would bring their formatted cards and return the camera or the device as broken when it won't read the exFAT fs so you'll have to support it) and you add a crapload of other potential problems for almost no benefit.

quoting from wikipedia:

Compatibility with SDHC

SDXC host devices accept all previous families of SD memory cards.[26] Conversely, SDHC host devices will accept SDXC cards that follow Version 3.0, since the interface is identical,[3] but the following issues may affect usability:

SDXC cards are pre-formatted with Microsoft's proprietary and patented exFAT file system, which the host device might not support. Since Microsoft does not publish the specifications of exFAT and its use requires a non-free license, many alternative or older operating systems do not support exFAT for technical or legal reasons.
The use of exFAT on some SDXC cards may render SDXC unsuitable as a universal exchange medium, as an SDXC card that uses exFAT would not be usable in all host devices. Since the FAT32 file system supports volumes up to the SDXC's maximum theoretical capacity of 2 TB as well, a user could reformat an SDXC card to use FAT32 for greater portability between computers (see below). FAT32-formatted SDXC cards can be used in a host device built for SDHC if the host device can handle 64GB and larger volumes.
SDHC host devices will not test the new capability bits defined for SDXC 4.0 cards. It will therefore not be able to use the new features of SDXC, such as transfer speeds above UHS104 (104MB/s).

Host operating system support

Microsoft Windows versions that support SDXC are: Windows 7, Windows Vista SP1+,[3] Windows XP SP2 or SP3 with KB955704,[27] Windows Server 2008 SP1+, Windows Server 2003 SP2 or SP3 with KB955704, and Windows CE 6.0 and higher.

Apple Mac OS X versions that support SDXC cards and exFAT are Mac OS X Snow Leopard 10.6.5 or later including OS X Lion 10.7.[28][29]

BSD and Linux systems that support SDHC cards also support SDXC cards that contain a compatible file system, but they normally do not support the proprietary exFAT file system that is installed on SDXC cards, because of patent issues. However, Google Code contains an implementation.[30] The user may reformat the card to contain a different file system (see below).

Need less than 32 GB : SDHC
Need more than 32 GB : mSATA, SSD ... 3cm x 5cm (about 1.2-inch x 2-inch) in size :