Not all the slab wing aircraft had the trim in the roof, the later aircraft had the trim on the floor.
I own a PA28-180 and the aircraft is very popular with the club that I lease it to because the rental cost is reasonable, the aircraft will do all that the Archer 3 will do in terms of the performance that the average club member can use.
But because it cost me about 15% of what a new Archer would cost It is a far more productive aircraft, yes the maintenance bill is a bit high at the moment but it won't come close to the interest payments and insurance of a new or an almost new aircraft.
Once the aircraft is fully sorted the maintenance bill will come down to just above the cost of a new aircraft having spent 25-30% of the cost of a new aircraft.
The simple fact is that a new aircraft won't attract 70% more income and even if the maintenance bill on the old aircraft is 5-10% bigger the numbers still make a late PA28-180 a very atractive aircraft for a market that has mostly VFR pilots and very few IMC holders who would chose to fly on a "hard IMC" day.