Any list that suggests the best, worst, most influencial, etc it extremely subjective. However, on a whole, I thought this list was reasonable correct. Is a song "best" because it has good lyrics or a cute melody or a great guitar solo or because it had an influence on people.
Some of us who are older were very much influenced by Dylan, the Beatles the Stones, etc. While some younger people may be influenced by Nirvana, Metalica, etc. I'm sure many kids these days are influnced by artists that I've never even heard of.
As far as too many songs from the 50's and 60's and lack of songs from the 80's - history can pretty well document that certain songs from the 50's were the start of rock and rock (which has influenced every generation to follow). Many songs of the 60's (most significantly the Beatles) helped shape an entire generation (which in turn shaped the future of politics, marketing and every aspect of regulatory and commercial commerce. Dylan made social comment within the text of song a significant part of music (more than anyone before or after). Thus the songs of the 50's and 60's deserve recognition.
Regarding the 80's (and forward to 2004)- while there may have been songs that had some impact on the youth of the 80's, 90's and beyond, there was little that shaped our culture or changed politic - with the exception of the continued growth of hiphop (and I question if that is a positive or negative impact). Personally, while there are post 60's artists who I enjoy, the last 20-30 years were void of any music that I could deem historically signifcant music!!