Due to selection restrictions of grid design it seems like making selection available just in rowexpander is not that bad solution.
I got it worked on other browser's except Chrome Version 23.0.1271.95 m.
Yes i got it worked even on webkit browser's too by adding -webkit-user-select: text !important;
Finnaly my overriden css looks like below.
.x-list-body dt EM,.x-list-header-inner DIV EM,.x-grid3-row td,.x-grid3-summary-row td,.x-grid3-cell-text,.x-grid3-hd-text,.x-grid3-hd,.x-grid3-row
-moz-user-select: inherit !important;
-khtml-user-select: text !important;
-webkit-user-select: text !important;