All of the magnetically locked doors in my building are released automatically upon fire alarm, but I understand the emergency door release boxes are available in case the doors fail to unlock during an alarm.

To access the office I work in, you have to travel to the 3rd floor lobby, freely accessible to anyone, and then swipe through a restricted access door with a security fob. To leave the office, there is a normal door release button anyone can use, as you are leaving a restricted access area, not entering one. 

The green "break-glass" style emergency door release box is located directly next to the door release button, on the inside of the office. But there is no emergency door release box from the lobby into the office. This is actually true for every other office in our shared building.

If a fire started in the main central stairwell attached to the lobby: a visitor, or staff member without their pass could conceivably exit into the lobby, only to then discover their route obstructed, and that they are now trapped there, unable to travel through our office to the alternative fire exit. 

On the other hand, the emergency release inside the office is only necassary if both the automatic alarm release and the standard release button both fail which seems doubly unlikely. Am I missing something obvious, or has our landlord placed all of these emergency door release boxes on the wrong side of all the doors? Is there a rule saying door releases are only required in the direction of exit? This doesn't seem to allow for the possibility that one route might be blocked. Should I ask the landlord to relocate these, or to install additional boxes on the other side of each door, and are they legally obliged to do this?

The placement you describe is exactly how it is usually done.

The concept is that you have failsafes so that you can be sure of getting out of your workplace and on to the escape route.

Putting them on the other side would be a security risk, as anyone could break the glass and get into the office.

The alternative escape route you mention is presumably a designated escape route from your office, but not a designated escape route from the main stairwell.