Yes, there are 4GB SD cards that are NOT SDHC. I have one of those. I think 4GB is the max size though ... and that too, those are rare. If you go any higher in size, it has to be SDHC.
Anyway, CyGuy (and others), Meritline has - what looks like - a Lexar MicroSD 4GB card that is not SDHC. I have ordered one of these last night (and looks like Ellen ordered one as well). So we will be able to confirm soon.
See the link in my post above.
UPDATE:
Here is the obligatory Wikipedia reference
that confirms that 4GB is the only size where SD and SDHC cards overlap.
http://en.wikipedia.org/wiki/Secure_Digital