Why did James have to die but not Lily?

[lily_paige_delaney]

No: HPFGUIDX 71256

I was reading the end of Philosopher's Stone last night and was 
struck by something Voldemort told Harry.  Voldemort says James 
fought a brave battle but Lily didn't have to die - as we know she 
died protecting Harry.  

We supposedly now know why Voldemort killed Harry (the prophecy) but 
why did he kill James?  We know that Voldemort only kills exceptional 
people (less important ones are delegated to the Death Eaters as 
outlined by Sirius early in OoP).

This got me thinking about another possible interpretation of the 
prohecy.  Remember that Voldemort only heard the first part 
(according to Dumbledore)  What if it could have refered to James 
AND/OR Harry so Voldy set out to kill them both to be sure?  We don't 
know what month James was born or what happened to his parents - but 
possibly they had fought Voldemort three times themselves and then 
been killed.

I also think its possible that Snape tried to warn James about this 
possibility to eliminate his life debt to James for saving his life 
and that James ignored him, hence Snape telling Harry his father had 
died too arrogant to believe he was in danger.  

So many possibilities and so much unknown!

LPD