different style of coding to reduce logic resources??

Case 2 has NOT the same behavior as case 1.

While the <= assignment inside always block is performed only at clock edges,

statement assign intr_wire = { intr_wire[0], intr } is a continuous assignment (I mean combinatorial, clock independent); then you actually get intr_wire = { intr, intr }

and a few resources are spared.

You should have written:

assign intr_wire = { intr_reg[0], intr }