Its a "Trust" issue, and quality links are the best fix (just like they are for pretty much everything else, but thats another story). Its not hard to rank right off the bat for "red widgets", or "blue widgets", or even "free widgets", but in any sort of competitive environment ranking for the main term, "widgets" proves challenging.
Why the easy acceptance for "red widgets" and total mistrust for "widgets"? Just from a purely mechanical, algorithmic perspective I always found that to be such an oddity. Google deems the site a trusted resource for information on "red widgets" but sends it to oblivion for "widgets".
This is fairly common, so its gotta be by design, but it doesn't make a whole lot of sense.