As mentioned by CDF, the Highlander is larger than the Santa Fe, and it is also larger than the Sorento.
It's silly to compare the Sorento and Santa Fe to the Highlander price-wise, since both are smaller vehicles.
The Sorento and Santa Fe are both smaller in-person than in pictures or videos, especially the Sorento. The Rav4 is closer in size to both of them than the Highlander is.
Also keep in mind, the Sorento is a brand new redesigned vehicle for 2011, and the Highlander will be getting a redesign soon, along with the Santa Fe also getting a redesign soon.
Yes, Toyota should definitely split the third row in the Highlander. I have no idea why they didn't do it in the first place. A terrible decision I think, not to have split the 3rd row in the first place. Hopefully the redesigned next-generation Highlander will get a split third row.