Hi, It sounds as though there was only one coat of finish put on. As Steve says also, it may have been a weak finish to boot. Unfortunately, it is my belief that the first coat is the most important, especially for pine because it is sort of "where the rubber meets the road". Also, to a degree, whatever hardness your finish, you will still have soft pine underneath. Sounds like you need 2 coats of a premium polyurathane. I tend to go for the old fashioned kind instead of the water based but I'm sure there are some good water based if you prefer. I start with high gloss and I finish with satin or whatever final appearance I want. This is b/c I feel the high gloss is harder. Again, with pine you are going to get some nicks. It might be best for people with pine trim to just beat it with a chain to antique it, and then they won't mind the occaisional blemish, just joking, sort of.
One "cheat" I swear by, especially for renters wanting to spruce up the appearance of scratched up and abused wood floors is "LIQUID GOLD". This is some magical juice that they sell in supermarkets etc. as a sort of pledge-like furniture polish or something. Don't buy the spray can, get a large tin of it. Wipe down your scratched and blemished brightwork (varnished wood) and the scratches will disapear. I think it smells good too. Wipe the extra off and dry so it won't be too slimy and collect dust. Voila! Good luck!