Old engines had poor power rating compare to now because they tended to be "peaky", torque was OK down low but the engine lacked power as RPMs climbed. That's where most of the power gain has occurred over the past 20 years, in the high RPM. Twin cam and VVT mostly led to more power high up in the revs, but not much gain down in the low and mid-range.
The Mazda Protege's 1.8L engine in 1990 had only 102 hp, which is basically 25-30% behind some of the 1.8L engines now available (for instance the Caliber's 148-hp 1.8L or the Civic's 140-hp 1.8L), but its maximum torque was 111 lb-ft, that's only about 10% behind what today's 1.8L engines get. Another clear example is the first Saturn sedan/coupé in 1991 with a SOHC engine that got only 85 hp (40% less than the 2007 Civic), but got 110 lb-ft of torque (only 13% less than the 2007 Civic), available as soon as 2400 RPMs. I don't think most people frequently make their engines rev up to 5000-6000 RPMs in normal driving, so the engines most of the time aren't that much more powerful than they were back in the early 90s or late 80s, but when we need to, we do have an edge with being able to play in the high-rev world like it wasn't possible before. Plus, cars were lighter back then, not something I whine about given the structural strength and safety of cars now compared to what it was before.
Addendum:
Remember, Power (hp) = Torque (lb-ft) times RPM of engine divided by 5252.
