ten years ago是过去的一个时间点,前面相应地用了短暂性动词（也叫非延续性动词）die.
His grandfater has been dead for ten years.
ten years是一段时间,前面相应地要用延续性动词.die的延续性动词是be dead.
非延续性性动词转延续性动词的规律
1、用意义相同或相近的延续性动词替代.如：
borrow→keep,buy→have,become →be,get up→be up,fall ill →be ill,put on→ wear,come here →be here,go there →be there,get to know → know,go (get) out →be out,fall asleep→ be asleep,get/catch a cold→have a cold
2、用“be+形容词”替代.如：
die→be dead,open→be open,end/finish → be over,
3、用“be+介词或副词”替代.如：
begin/start→ be on,join→be in/be a member of,leave→be away,come→be in/here,go→be away/out,reach/arrive/get to→stay/be in