I've worked on several large blogs, and yes, there's definitely a business plan. The interesting thing is that a lot of the Gawker/Mashable-style blogs do run on ad models, which hurts them in the long run, because they are forced to cram in extra ads and annoy the user a bit (Take a look at newspaper sites as well - a lot of these brands have never thought about ways to make money beyond selling space, which is why you end up with page takeovers and popups galore). In order to be really successful, it's better to have a secondary product or line of products behind it.
One example - in the past I worked for a large digital marketing site. The blog bought in all the traffic, powered the social, gained recognition and exposure, and positioned the business as experts in the field. The company also ran training, published research and ran events - conferences, roundtables etc.
In the case of a roundtable, you'd do a survey to find out what people's problems were - issues with mobile marketing say. Then you'd have a piece of research based on that. You could then hold a roundtable or event on the subject. Then you could write about the figures in your research, and the conversations at the roundtable, or the presentations at the event, and you'd get a lot more insights. If there's enough interest, you'd run training on it. Each element of the business helped all of the others work as well. This meant you could produce sponsored research, have co-branded events etc, and you wouldn't have to rely on tons of ads and affiliate stuff everywhere. And of course, all of that is quite scalable because you can put it in a subscription package.
It is possible to do but in practical terms, you often need to make a decision about content. You could be going for a big SEO push, or you might want lots of shares (These are tied together quite closely though, so you can do both). If I wanted a car blog that was mainly focused on SEO, then 'd head to Google Keywords, and find a couple of hundred keywords related to cars. A quick look shows "Second hand cars, car auctions, car buying, car dealers" are all quite popular. Then I'd put them in a big sheet and turn them into headlines. "15 interesting facts about car auctions that saved me $10,000" or something. I'd want about five posts minimum on each keyword, and away we go. Or I could go for sharable - BMWs CEO talks about how making a slower car made them $50M - which is more B2B focused, so you'd have a chance to work directly with larger businesses. This is a bit more important these days because there's a LOT more noise out there these days. It's difficult to cut through but having a niche can really help.
Lifehacker is an interesting example, because they've clearly cottoned on to co-branding and affiliate stuff. So you get 'the ten essential camping items' and stuff. Writing actually useful promotional stuff is difficult, but it can be done, and done well.
PPC depends on your niche. Some subjects won't scale well as google ads - particularly if you were targeting some niche B2B markets, where there just aren't enough relevant people, but if you're selling T-Shirts, then hey, everyone is a customer right?
Scaling is tough, and generally all these sites underpay the writers, because business models have trouble understanding that just because you can't put a credit card number into Twitter, it doesn't mean it's not making all of the money, but put it this way. if you can put $1000 into social ads and have people click through, who generate $10,000 of affiliate revenue, then you really ought to be sticking $10M in to social ads ;)