Chris, when you say ships of the same class don't have to be exactly alike, are we talking internally, externally, or both?
I believe both. Let me list some examples:
Check out the bridge of the Odyssey, the doomed Galaxy-class Starship in "
The Jem'Hedar" [DS9]. Don't you see how different its bridge looks? It's more tech-like than the comfortable Enterprise-D bridge. Then there's the more-subtle changes like a different color scheme and probably some additional stuff here and there of the Yamato (from what little we saw of her in
"Contagion" [TNG]), all these support that there are some differences between sister ships. They can be subtle or they can be significant. We only
once had a look at the Venture, and it supported Phaser strips on the warp nacelles. This was due to an error of course, but an error made to be canonical. These starships can have some changes both in and out. Also, some Galaxy-class Starships during the Dominion War had some subtle differences, like some changes to the hull (around the neck, possibly), lit-up names, or even Deflector Dish color changes that indicate a possible upgrade of the Deflector Dish.
The Nebula-class Starships had some differences here and there. Most notably is the differences between the "Proto-Nebula" U.S.S. Melbourne seen in
"The Best of Both Worlds" [TNG] at Wolf 359 was built to have two miniature nacelles, no pod. Then there's the U.S.S. Phoenix (
"The Wounded" [DS9]) with it's round pod supported by two pylons and the Shuttlebay had clear access. In
"Redemption, Part II" [TNG], we saw the U.S.S. Sutherland, the most notable difference being what we know as a "standardized" Nebula-class, the single pylon-supported triangle pod being common. Also, we know it not to be an upgrade due to what action we saw in Wolf 359 at the beginning of
"The Emissary" [DS9] when we saw a standardized Nebula-class and an Ambassador-class making a sharp turn and engaging the Borg Cube after the Saratoga was caught in a tractor beam.
Speaking of the Saratoga, let's look at Miranda-class Starships too. Check the different bridges of the 2280s-era Miranda-class Starships: Ever noticed some differences between the Reliant (
"Star Trek II: The Wrath of Khan") and Saratoga (
"Star Trek IV: The Voyage Home)? Assuming neither had some refit that makes either sister ship more updated, you'll notice some difference in stations. The same with Miranda-class Starships in the 2360s, if you pay attention to some TNG episodes (The Brittain in
"Night Terrors" [TNG] for example) and the DS9 pilot (the Saratoga from "
Emissary" [DS9]). Also, note how the Lantree (in
"Unnatural Selection" [TNG]) had no roll bar sporting weapons whilst the Brittain (
"Night Terrors" [TNG]) did, whilst the Saratoga at Wolf 359 ("
Emissary" [DS9]) sported two strange devices or weapons on each side of the ship. I won't include the U.S.S. Bozeman (
"Cause and Effect" [TNG]) as this Miranda variant is actually a different class of Starship, strangely enough. The different class in question known as a Soyuz-class.
How about the Constellation-class? The U.S.S. Stargazer (
"The Battle" [TNG]) and the U.S.S. Hathaway (
"Peak Performance" [TNG]) had some differences in the interior areas at least. It's evident due to the main bridge configurations, if you had a good look.
Constitution-class Starships aren't all alike either. The U.S.S. Constellation, NCC-1017 (or NCC-1710 in the
Starfleet Museum as I prefer), had some different details and hull dimensions here and there. The real life reason of course is due to the usage of an AMT model for budgetary reasons when making the episode
"The Doomsday Machine" [TOS]. But since it's on-screen, I'd say it's canon.
So I believe the Defiant can be accurate just by being as it is.
(Edit: Okay, I give up. I really give up in this personal issue, to which I'm cutting out of this message. Rat Boy, I apologize for being rude when I felt one of your posts was insulting. I won't do it again, I'll shut my big mouth and try keeping it shut. I'm sorry. I hope this settles the personal situation we've had for the past two days.)