I was wondering if someone could enlighten me about the differences between the silvretta 404 and the silvretta 500 bindings. Are the 404's less safe or have any drawbacks that the 500's have fixed? thanks!

Check this:
www.wildsnow.com/bindings/silvretta-500-backcountry-skiing-b>>>

so, from that article, it seems like there was very little changed beyond the aesthetics and lighter materials. i noticed the lateral release looks different too.

Yes, I think you are right. I use the Silvretta 500 and I like them because they accept all types of AT boots. But modern dynafits might be lighter, however I heard that they also may unclip when the front wholes in the boots wear out. I am not sure if this is true. I use TLT 4 dynafit boots with Silvrettas and they work great.