Buenchico, I'm afraid from experience, I'd beg to differ.
There is no reason why a wifi dongle would not work with a Smart TV. I note you wish to emphasise LG models, but I can confirm that the LG webOS is of no significance in these circumstances. Dongles do work in this situation. They don't require any Windows OS. I infrequently plug in a Belkin dongle into the LG and it functions perfectly adequately and having used it on other Smart TV models such as Panasonic, Toshiba and Sony amongst others, I can assure you it works. In fact, I've not come across one that does not function in these circumstances.
Turning to the issue of Ethernet connections on Smart TV's, I can accept your surprise in this day and age of omnipotent Wifi. Regretfully, I can't agree with your view on "modern" laptops and Ethernet connections. I'm typing this on a two grand plus MSI GT70 2PE Dominator Pro which is an extremely high spec gaming laptop less than one year old and yes, it has an ethernet socket. My run-of-the-mill Acer also has an Ethernet socket and that's six months old. In addition, my Samsung colour laser printer (ClX 6260 series, 9 months old)