Because if units can't pass through cities, you would need to surround every city with roads, what would take too much time and too much maintenance.
When did they ever say that units can't pass through cities?
Its ridiculous to think you'll need to surround the city with roads.
Just think of the city as another unit under 1upt; you might not be able to end a turn in it, but you can move through it just fine.
f units can go through cities, there would be a problem of congestion that would make you stupidly loose turns of production because there would be one unit in the cities on the verge to create a new unit.
There might be congestion if you're moving large armies over a single road, but I do not see how you can possibly conclude that you'll lose turns of production. You can move a newly created unit to any tile in a 2-hex radius - more along the roads. THat's a huge number of tiles.
So how are you going to lose production???
Beside that, I believed that units were not allowed to defend cities anymore, so it would be impossible to put them in a city. Seems contradictory with another information that said that there would be one unit allowed in the city.
I agree that there is some confusion here (though note; you don't need to be able to have a unit *in* a city in order to pass through the city via a road). Though its entirely possible that you'll be able to have one unit in a city (newly constructed, or "merging" it with city) but also not have it defend (like civ4 naval units in a city), or have it defend first (before the city - its camped outside the walls) but with no defensive bonuses. Would still be a bit weird though.
I guess you would have to spread your army all over your territory
Right. Or probably a mix of along your borders and then a central reserve force. Keep in mind that armies will be much smaller than Civ4, so you probably won't have *that* many units.
The first said clearly that roads was useless for unit movements, the other claimed that roads will be indeed usefull in that regard.
I agree again that there is some confusion here, though I tend to believe the "will improve movement" is more likely since it came from a (admittedly potentially translation-mangled) developer interview, rather than a fan report from a convention.
But either case is feasible, and neither has intrinsic game-breaking problems.