As Wayne mentioned, Delaware gets lots of taxes from the corporate world, but that generally goes towards offsetting the lack of sales tax in DE. The reason property taxes are different between boroughs/townships of PA and DE is due to how schools are funded. The biggest portion of your total property tax is most likely from the borough you're living in, which is where school taxes get collected. Generally speaking the boroughs in PA with the higher borough/township millage rates (read, property taxes) also have better schools. On average, the public schools in Delaware would be worse than the public schools in areas of PA with higher property taxes.
If you're going to have kids, it would be worth it to pay the higher taxes for a better quality public education. Parents in DE generally would send their kids to private school for a better education, which far exceeds the extra cost you're paying in taxes.
If you're not going to have kids, then you're paying for other peoples kids to have a better education, which does have ancillary benefits for the area. Areas with a more education population generally have lower crime rates, and better quality of living.