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Newer style furnaces run similarly, longer runtimes at lower fuel usage, generally the blower speed will be variable as well, this can bother customers used to that blast of hot air coming out the vents.

Basically the lower supply temperature allows your boiler to condense the flue gasses more, that is where a lot of the listed efficiency ratings are coming from, without condensing you might only be running 80-85% instead of 93-95% efficiency. The boiler modulates the burner, so while it might run for more time throughout the day, it won't be using more fuel than a system that runs less amount of time but cycles more, assuming all other things are equal. If one system is condensing, and the other is non-condensing, the condensing system will use less total fuel (less wasted energy going out the flue pipe) but the delivered btu/hr to the space should be the same over a day's worth of run time. With a condensing boiler install, or a modulating furnace, I like to see that system running at a low fire rate for a long time, while maintaining the indoor temp at the thermostat setting. When modulating forced air furnaces were a lot less common we used to get calls from contractors wondering why the furnace never shut off, so you are not alone being confused by this!

If you are running a fairly low heating curve setting your system may not recover quickly from temperature setbacks so do keep that in mind. The required water temp to maintain 70 degrees, is different than the required supply temp to raise the temp of the space several degrees. I do a 2 degree setback when I remember to dial back my thermostats (I don't have programmable stats) and don't have issues recovering from that. Temperature setbacks are one reason many contractors in the US set these condensing units to run at max temp on install, but then you basically have a modulating 80% boiler instead of a 95% one. Don't be shy to raise the heating curve if the system doesn't keep up. your comfort level should come first imo.