I think its a combination of randomness and the amount of traffic that runs through a store. If one store has a total of 100 lottery tickets sold a day and another store sells 500 tickets, it is more likely to have a winner because they have more tickets in the pool of possible winners. Same thing as when they have a raffle....some people buy more because they want to be entered more times, thus having more of a chance to win....or if you decide to buy one MM or PB ticket verses 20. I think that's how it works. Now how well this fits into statistics and all that stuff I have no idea (I passed that course by that skin of my teeth in undergrad).
I know in one of my favorite stores I've seen people drop $100 on $5-$20 scratchers looking for the "big one". They just stand there and scratch and scatch until they are satisfied. So that store is obviously going to go through some of their games faster and need to be replinished sooner, thus giving that store more chances to have a JP winner. That same person who's scratching away will also spend 5-20 bucks on MM. So if you have 20-50 people comming in the store and doing that on a regular basis, I think it's more likely for that store to possibly have a winner. Maybe that's what's happening with the stores you've talked about having jackpot winners.