One thing to notice is that the open-sourced version of Qt is under GPL/LGPL, which means if you statically linked it into the executable, your application is then infected by (L)GPL.
Your application is "infected" if you use Qt without a commercial license, regardless of how you link it. It's a little harder (but still possible) to comply with the LGPL requirements when you statically link, but you are bound to those requirements either way.
Right, my point is that static linking is also okay with the LGPL, albeit slightly more difficult in terms of what you have to make available to end users.