The vast majority of single digit millionaires are doctors, lawyers, construction company owners. I've even personally met a factory worker who retired with > $1mm in savings due to prudent money management (no lottery wins, just basic financial management for 30+ years).
I live in a completely unremarkable town and there are loads of millionaires around. I bumped into one recently when I accidentally stumbled onto his property while hiking. Judging by the sprawling estate he's at least in $5mm+ net worth range. What does he do for a living? He owns an earth moving company. That's right, at the ripe age of about 45, he made tons of money moving dirt from one spot to another. Lovely guy too.
My friend from high school is also in the millionaire club. We're both from a public school background. Unremarkable back stories in just about every way possible. Now he runs a very successful web agency. He's super smart, hard working and I'm sure that accounts for the majority of his success.
My point is that there are loads of millionaires around, even in my little backwater. Far, far more than there are lottery winners. Seems to imply that luck plays a far smaller role in the success of millionaire next door types than simple hard work.