parasitic fringe capcitance calculation
The operating angular frequency for VLSI chip is high compared to Physical dimensions of the METAL1 Layer, thus the metal layers are considered of infinite length for effective capacitance calculation.

Here is the Capacitance Calculation for Cylindrical lines.As stated by you the formula 
$$
C = \dfrac{\epsilon \cdot  h \cdot l}{d}
$$
is used only and strictly for sheet capacitors.Here the METAL layes act like line charges.

Secondly since the routing of metal lines is done in very compact way there is an effect called crosstalking