I wouldn't necessarily say that Train fans "look down on" the Hogwarts Express sets...at least I don't. Personally, I think they are a great set when taken for what they are. They aren't designed to be a D2C direct representation of the Olton Hall engine. What they are, as others have stated, is a nice little set that captures the feel of the Hogwarts Express while still using pieces and building techniques that fit in with the age group (8-14) they are targeting with the set. An 8 year old isn't (generally) going to be able to build something to the level of the Emerald Night. Additionally, they have a price point to hit and these sets do that.
What I love about all of the Hogwarts Express sets is that they give you a starting point to work from. If you look at the version I built, I pretty much took one of the standard sets and set about modifying it to my liking. That's the beauty of LEGO.
So, I don't (nor do I think we should) look down on the standard Hogwarts Express sets. They serve a valid purpose and, if anything, I hope they encourage the younger (8-14) builders to take a look at trains.
- Davey -