I'm posting this as a new thread because it's already been marked by design, but if you look at the images it's certainly NOT by design, you've left something out, and the images make it very obvious. Click the image. The chat windows on the  left have bigger fonts but look way better than the NPC dialog box. Top images are on a 27" monitor, bottom on a 34", no difference. Whatever makes the left text look good, do that for the dialog box. Thanks @Jason_M for the tag.