I think I have an explanation then.
It looks like there is an alternative way of registering filetypes which is used by Notepad2. Maybe this is new to Windows7, I don't know.
Traditionally HKEY_CLASSES_ROOT is the merged display of HKEY_CURRENT_USER/Software/Classes and HKEY_LOCAL_MACHINE/Software/Classes, where settings in HCCU superseed those in HKLM. Things are then handled like you describe, a suffix key (ie .txt) points to a filetype key (ie text_file) and there you find shell/open etc.
All this is still true and in my case points to Windows Notepad. So D-Fend is seemingly correctly assuming that Windows Notepad is the default editor for text files when it reads file type asscociations the way you describe.
Still in Explorer Notepad2 is used. Strange...
After poking around in the registry I found something I didn't know before: under HKCU/Software/Classes/Applications there is a key called Notepad2.exe and under that some subkeys with the usual shell stuff. So obviously Explorer uses this key.
Now all that was missing was a link between .txt files and this HKCU/Software/Classes/Applications/Notepad2.exe key.
This link, I think, I found under HKCU/Software/Microsoft/Windows/CurrentVersion/Explorer/FileExts. There you find a list of filetype suffixes similar to the one in HKEY_CLASSES_ROOT. Under ".txt" are some subkeys with all applications that are capable of opening txt files and an MRU (most recently used) subkey that might be the one that determines the actual application Explorer uses to open the filetype.
I'm not sure, whether I describe the mechanism to its full extend here and unfortunately I couldn't find any MSDN page or similar describing it. But I haven't searched very long, so maybe you have more luck.
One thing though seems clear: This method seems to 'overrule' the 'normal' file type associations that you read from HKEY_CLASSES_ROOT.
Edit: Here you find some more information (in German): http://www.wintotal.de/tipparchiv/?rb=3010&id=1622 , although this is not exactly the same.
Edit2: I think the method described here is used by Explorer when one changes filetype associations via the context menu ("Open with...") of a file. In this case the traditional HKCR settings stay the same, but settings in .../FileExts are changed.