Can somebody please explain this. How close do you need to place houses to structures that requires workers? I have plenty of people living in my city but no one wants to work in my granary, work camps etc. I have a connected road from them and to my houses.

If there's a roadblock between the granaries and your housing, then the game won't give the buildings workers. I always recommend having your industry like this a small bit away from your main housing block and just giving it a 2x2 crude hut to get workers from and roadblocking all this so that your bazaar buyers or other people who provide services don't walk into these undesirable locations to provide useless goods to a house that is unlikely to evolve. When a labourer passes by a house, the people from every other house "flows through" your hut. Not very realistic, but it works :)

Is that a bug? As i recall roadblocks doesn't prevents workers getting to work in the later "Zeus: Master of Olympus" game

It's not a bug, that is how the developers designed the roadblock to work in Pharaoh. Plus, you don't have people wandering to their work in Pharaoh: buildings just send out a labourer and if it passes a house, the building will gain workers.

In Pharaoh, each building that needs workers sends out a labour seeker. If you watch you will see him emerge from the building. and can see how far he walks.

He only walks a certain number of squares before returning to the building. If he passes houses during his walk, the building will get labour. If he doesn't pass any houses the building will have no labour.

For the ultimate answer, what about this?