Only if a solid wood door is over 7 1/2 feet high or 36" wide will it have to be 1 3/4" thick. Solid core doors that size and greater are typically only 1 1/4" thick and are used in multi-million dollar homes.

Common install of interior jambs on 1-3/8" interior doors is generally with gun finish nails. Heavier exterior jambs are usually set w/ screws because of the extra weight of 1-3/4" exterior doors. If your builder is gong to use the heavier doors interior, they will want to use screws that go into the framing members behind usually through the hinges on the hinge side.

The "feel" of a solid door is very different from that of a much lighter door, which is usually hollow-core. The difference in "feel" of solid wood as opposed to engineered is IMO minimal. If you paint, engineered doors are fine; for staining, be careful to get the appropriate veneer to match or contrast with other wooden details.

Consider where the door is being used. If you can afford it, you will likely prefer solid or engineered wood on the BR and bathroom doors. Closets and interior doors to the basement will feel okay if in a lighter weight. Do be aware of paneling designs to be sure they match, regardless of weight. BTW, solid or engineered is usually considered more sound-proof, just as a thinner door will transmit more sound than a thicker door.

Hinges have a great deal of influence on the "feel". If you can find a place that showrooms a variety of doors, try them out and note the hinge as well as the composition of the door's material. BTW, I live within driving distance of 4 (yep, four) HD's. Only one has a really good display of the available doors.

here are the solid wood doors we used. we love them and people comment on them favorably! Come prefinished and with good quality hardware.

Here is a link that might be useful: Home Tec Doors

All of our 32 doors are 8' high, various widths, and 1 3/4" thick. 8 are solid alder and the rest are pine. I looked at a lot of doors and ended up having these custom made. I love them. On the closet doors I put mirrors on the outside, held in by trim in case it gets broken and can be replaced. below is a picture of the bedroom door to the left and the closet door to the right.
Everyone comments on my doors, to me they are at the top of the list of "glad I did it" in my new home.

Thank you all for the feedback. I am on vacation so I haven't been as obsessed with Gardenweb, but I was able to check in for a bit tonight. I love all the input. Thanks.

Our solid wood exterior doors are 1 3/4", but the interior fir solid core doors (standard height) are 1 3/8". I'm thinking maybe yours are taller if your builder wants 1 3/4"? We've only had hollow core doors before...We love the solid.