The outside is different. IIRC, one was originally a 10k model but when it was pointed out that the interior layout was identical to a 7.5k model, the price was dropped.
Be sure to note what features they have. I bought one in Kalavana for the dark patch but it didn't have one. It had fireflies and herb garden and maybe barnacles, no peat, no dark patch. All have herb gardens I think.
WOW. Look at all that space in the first 5k bog house... I had no idea. If it weren't for the 12 herb plots in my home, I would considering moving for all of that real estate.
Yeah that first 5k house has a fantastic yard. It was my first home in the swamps but I had to upgrade to the 7.5 for the extra room space. Still miss that yard, though. Also the wormbowl. The 7.5 totally needs a wormbowl.
I have the type 2 5K house and I love it. It doesn't have a ton of yard space, at first I thought that would bug me but I kind of like all the different levels, but the edges have nice hidden spots for hiding my hoard. Also I really like fireflies at home, and wormbowl! I did want a 7.5K house for more herb plots but they were all sold out when I bought.