ask偏向“问”
1. May I ask a question?
我可以问一个问题吗?
2. I have asked some friends for tea.
我请了一些朋友来喝茶。
3. Did you ask the price?
你问价钱了吗?
ask for偏向“要求”
1. The people ask for political asylum.
人们请求政治避难。
2. B: You should ask for a refund.
你应该要求退款。
3. What more could they ask for?
他们还想怎么样?
所以例句中的for不可省略,否则意思不对
参考资料:http://zhidao.baidu.com/question/63227589