Rachel, the model you bought is being sold off at clearout prices. TomTom is replacing this with the '3rd Version' (or whatever) which has no SD slot. As another poster suggested, this is a 'stripped' version of what you bought in order to create a low-end model. This will force those who want the expandibility of the SD slot to have to purchase more expensive models.
So believe me, you are far better off with the SD slot as you can bypass the built-in 1 gb memory if you need to. Yes, your maps are older and are not compatible with Mapshare, but I don't think any One users are getting updates sent to them anyway as of yet. And I have seen elsewhere that this may not be a free service!
Enjoy your TomTom and sometime in the future, you will be able to purchase the newer maps (if you find your v6.65 maps inadequate).