I don't want to get into the railroading debate again. Suffice to say, I don't believe railroading is bad. Also, nearly every thing a DM does is "railroading" by at least one definition of railroading.
I don't believe the situation is railroading, it doesn't force the PCs to do anything. It only limits their options. They have the option to talk to the bridge keeper or they have the option to turn around and go back. They have the option to trick the bridge keeper into letting them past or bribing him or negotiating or threatening him or complimenting him until he agrees. They can take the long way around the pit, finding a way that doesn't involve crossing the bridge. They can kill him and walk over the bridge.
All I want to do is limit their ability to bypass my NPC entirely.
This is all fine and dandy until your players find the loophole in your campaign that you didn't notice that allows them to skip 6 months of storyline you were planning for your campaign. Especially, if you wrote up extensive notes and maps, along with made NPCs and planned out monster encounters for that time.
I've had it happen 3 or 4 times now. Each and every time I had to resort to an Out of Character discussion with the party about how I didn't foresee them having that ability or trying that tactic and that it will cause too much damage to the whole campaign if they take that action. So much so that the storyline will be no fun for me, as the DM. And I refuse to run a game that isn't fun for me in addition to the players. So, I gave them 2 options...the only ones I could come up with: Take their action back or have someone else come up with a campaign and spend the effort to run it.
They took it back.
Luckily, I haven't had to have that conversation with anyone since 4e came out.
It's not about taking away free will, as I mention above. It's the difference between running a cop game in modern day earth...and an equivalent game where one of the characters is superman.
In the first game you can decide in advance that the villain killed the victim and is hiding out in a house on the south part of town. You can anticipate that the group will track down clues, talk to witnesses, eventually track the perp to his house, and have a shootout as the perp has a gun. But that the perp had an accomplice who there is no evidence of in the house or alley..so he'll be around as a villain for next time. You can then safely draw a map for the shootout, create stats for the perp and his accomplice, create the personalities of the witnesses as well as the gang member who knows what the perps name is and even start thinking about what kind of crimes the accomplice will do in the next adventure.
In the 2nd game, superman simply flies around the early until he reverses time to the point where the murder happens. Then stops the murder from ever occurring and catches the perp and his accomplice at the same time. You then have to throw out everything you had planned to do.
Saying "I don't want superman in my game, and I'm not going to allow it" isn't railroading anyone or taking away their choice. It's saying "I'd like to play a game that doesn't have to deal with the abilities of superman. I don't want every villain to have to carry kryptonite in their pockets just to have a game that I can keep some control over."
And that's what you have to do with a Wizard around. Every villain has to have the resources to block scrying, teleporting, death magic, invisibility, flying, dimensional traveling magic, and so one and so forth. Put it all together and it might as well be Kryptonite with how rare it SHOULD be, but how common it turns out to be, simply so that the Wizard doesn't have to be any less powerful.
Also, not sure where you're getting this one. The pathfinder version of teleport AND the 3.5e version are exactly the same in this case: You can teleport yourself and one extra person per 3 caster levels. A party of 4 can be teleported at 9th level(12th for a 5 person group). And by the time you are 12th level, with the bonus spell from a high stat, you can cast 4 of them a day, so you can go back and get another 4 people if your group is larger than that. I'm not talking about Epic games. I'm talking about 12-18th level games.
We had a wizard who was 14th level who used to teleport back to his house each night from the dungeon just so that his butler could make him a home cooked meal in the morning. We had 6 players in our group, so he regretted that he couldn't bring us all back. But he assured us that he'd bring us some scones.
Yeah, the reason they stop at that level is because the system doesn't handle high levels well. Mainly because of spellcasters and their ability to ruin any adventure you come up with.