There's no requirement to state country of origin on processed foods (it has to be labeled on unprocessed fish and shellfish at present, and in 2008, it must be labeled on meat and perishable agricultural products such as fresh and frozen vegetables).
A better rule of thumb would be to look for processed food (and all canned or bottled items fall into that category) that states "product of the USA." Most processed food doesn't state where it's from, because it's not a requirement.
I also wouldn't assume that the cheap/house brands are necessarily imported. I was in Whole Foods yesterday, and looked at six or seven different brands of canned peas, most labeled "organic." Only two had the country of origin labeled: the cheapest house brand was the only one I could find that was labeled made in the USA. The other brands -- some three times as expensive as the house brand -- might be made in the US, but by not labeling it, the manufacturer has the option of using produce from anywhere in the world, without the expense of reprinting the labels.
Thank you for this information..I will pass it along.