The installer doesn't enable any themes

If you do a a fresh install and go to "Administer > Site building > Themes" you will see that all themes are disabled including the default one.
It is not a display problem: themes are actually disabled into the database -- status = 0 into system table.

The selection of the default theme is done in system_install(), but it is not enabled :

  db_query("INSERT INTO {variable} (name,value) VALUES('theme_default', 's:7:\"garland\";')");

  db_query("INSERT INTO {blocks} (module,delta,theme,status,pages) VALUES('user', 0, 'garland', 1, '')");
  db_query("INSERT INTO {blocks} (module,delta,theme,status,pages) VALUES('user', 1, 'garland', 1, '')");

IMO the easiest fix would be to add there a line to also enable it:

  db_query("INSERT INTO {variable} (name,value) VALUES('theme_default', 's:7:\"garland\";')");
  db_query("UPDATE {system} SET status = 1 WHERE name = 'garland' AND type = 'theme'");

  db_query("INSERT INTO {blocks} (module,delta,theme,status,pages) VALUES('user', 0, 'garland', 1, '')");
  db_query("INSERT INTO {blocks} (module,delta,theme,status,pages) VALUES('user', 1, 'garland', 1, '')");

As this looks kind of hardcoded, I thought that install profiles could be a good place for default theme selection.
This would allow for greater per-site flexibility, but I am not sure if this is an acceptable solution.
Anyway I have quickly tried to add these lines to default.profile and they work good:

  $default_theme = 'garland';
  db_query("UPDATE {system} SET status = 1 WHERE name = '%s' AND type = 'theme'", $default_theme);
  db_query("UPDATE {blocks} SET theme = '%s'", $default_theme);
  variable_set("theme_default', 's:7:\"$default_theme\";");

Thanks for any comments and opinions.
Riccardo