I think the respective regional dates are reasonable averages of when the weather turns and is consistently halfway decent, most days, most years. Late March/early April in PA can run the gamut though.
We usually go to camp (Potter Co.) the first week in April for a Spring work trip, and to help with the local stockings of the creeks near the cabin. My Dad and I have stayed a couple extra days the last few years to try to fish the special regs areas, but the weather's been garbage. VERY cold, below freezing, and snowy more often than not. VERY high flows too. We've ended up not fishing much, and when we did, the conditions were rough. We bailed on that this year and are just going up for a couple days to do a little work and help stock. Figured it makes more sense to save the couple extra vacation days for better weather/conditions.
In the northern tier counties, you can make a good case I think that it's not consistently above freezing until the second half of April many years. (I saw low's in the upper teens across the northern tier of PA when looking at weather reports this morning.) In the SC and SE portions of PA, it's probably closer to April 1. Overall, what's in place makes sense I think.