The column width information is not recognized when importing a formatted table, as you've seen, and I don't think there's any way to retain it. You'll have to reformat the table after it's been imported. Table styles also don't define column widths as part of a style so applying them won't work either.
Interesting, because when I import an Excel spreadsheet that was created by another person, column width is maintained. It would seem there is some different between the two Excel tables, I just don't know what.
Don't know, if that helps, but what you can do is converting a table to text. Then apply a paragraph style with tabs set to different values. Then again convert back to a table. The tab positions will be recognized and will form the width of the columns.
1. A table with uniform column width
2. Converted to text, tab positions set
3. Converted text to table