Why did he say "Mah She'elasech
Vilna Gaon: She'elah is for herself (what she lacks); "v'Yinasen Lach" applies to it. Bakashah is for others; "v'Se'as" applies to it.
Malbim citing Meforshim: She'elah is the request itself. Bakashah is the purpose. E.g. one requests money; the purpose is to buy a vineyard.
Malbim: She'elah is a small request that is granted easily. Bakashah is a big request that requires much supplications. Whatever the queen will request for herself is called She'elah. She need not supplicate. Surely he will not refuse her! Initially he said "u'Mah Bakashasech Ad Chatzi ha'Malchus v'Yinasen Lach" (3). He called a great request for herself Bakashah. After he promised this, she need not supplicate for even a big request for herself; it is She'elah. What she requests for others is Bakashah; it needs supplication, for he did not promise her about it.
Why did he say "v'Yinasen Lach
Malbim (3): Initially, he intended to give only if he asks for herself. Now, he offered even if she asks for others.
