I have two devices. My old one boots to SD very reliably. My new one is very temperamental. But it will boot eventually. For me it just takes many, many tries. I finally got it to boot, did a nandroid backup, then flashed the emmc CM10.1 and the emmc CWM. So now I never have to boot to SD again with it. All flashing can be done with emmc CWM.
Edit: If you want to stay with stock and still be able to flash my mods, you can just flash the CWM that gets put on internal memory (emmc) so that you don't have to boot the SD CWM anymore. I made a custom version (6028) for internal memory. You can get it
here or
here. That just means it cannot be auto-updated to a new stock. After you install this internal memory CWM, you get to it by holding the n and power keys together on boot and releasing after a few seconds. It should boot to CWM. If you want a new update to stock, you would need to flash it manually with CWM. If you do update, you will need to re-flash the emmc CWM again immediately before re-booting since the update replaces CWM with stock recovery.
Sent from my Nook HD+ running CM10.1 on emmc.