[SwellJoe]

C64 had better graphics modes available. It had higher resolution and better color availability (same number of colors, but the C64 could use more of them in a smaller area). The C64 had quite powerful, for the time, dedicated chips for sound and video, including providing hardware sprites, which took a lot of load off of the processor (a very similar CPU was in both the Apple and C64), so the C64 could do more on screen at once.

Also, because of the popularity of the platform, developers knew it really well, and were able to utilize tricks to occasionally go above and beyond expectations (for example, it's possible to get a lot more than 16 colors out of the C64, particular in still images). These undocumented modes and techniques became pretty common knowledge through the several magazines that covered the platform, and through various demo/warez scene channels (like bulletin boards).