If the Price winner can do that with Sigma, it doesn't the rest of the len are pointless: He used multiple exposer ... to get the kind of image with post processing skills and the ability to use Filter effectively... that only landscape .. he did it at the right place, right time, with the best of his skills and equipment..( He can even do better than this, I think, yet he pictures are already great)
There are equally bad pictures taken by the Sigma 1770... at some instance: Sometimes I am afraid to use this len under low-light conditions.
You definitely can take great pictures with the kit len: .... but I think it also about the purpose of the len, what it is good for....how you handle it, your artistic inclination and inspiration what do do want to get form the picture you want to take.
Every len has it sweet spot and down end including great len... I think if you know the purpose and what you expect to produces and your ability to deliver the results is one of the key to great pictures.
I came across one great landscape photographer said that you will get relative good pictures with relative good equipments, if you understand the magic of light, your images will stir the soul.
Good len is really good len: you want know until you put them to the tasks...it actually eliminate post processing and produce more organic quality pictures...len has characteristics, different photographer has different preference on what len they prefer to use, that they think can give them the best results.
I think these people inspires others that you can also do even better with relative better equipments.
http://www.flickr.com/photos/nc_chia/