Eh, it's more a matter of geography and the numbering of the interstate system.
East-West interstates are even numbered, with numbering starting at the south and moving higher as you go north.
North-South interstates are odd-numbered, with numbering starting in the west and moving higher as you go east.
So Disneyland, being in the southwest of the U.S. is surrounded by low-numbered interstates on all accounts (I-5, I-10, I-15).
WDW, being in the southeast has low-numbered east/west even numbers (I-4), but high-numbered north/south numbers (I-75, I-95)
(And compare that to here in New England, where all of our Interstates are high numbers: I-90, I-93, I-95, I-89, I-81)
You want something a little more freaky-coincidence, both Disneyland and WDW are in Orange County in their respective states... (Well, most of WDW is, at least)
-Rob