I see this parroted a lot, but I have yet to be convinced. I guess it really falls on what level of scoring you require for a line to be considered to be a 'scoring line'. Teams this year that I'd consider to have 3 scoring lines: Washington, Dallas, LA, Tampa, Minnesota, St Louis ... I can go on. Chicago in 2010 absolutely had 3 scoring lines, arguably in 2013 as well. Last year they shifted between 2 and 3 scoring lines as Quennville saw fit. As you can see, lots of different styles, but all of those teams tend to play 3 lines that are a very health chance to score when they're out there. Minnesota is the most questionable of my list, but when they're 'on', they're playing a 3 scoring line sort of team.
For me, a 'scoring line' is a line that's a threat to score, not necessarily one scoring every game. Minutes? Play the hot hand, give minutes to the line that's playing well. Not to mention it lets you cut back on minutes for a weak 4th line that can only get the puck out and do not much else. I think it's very much possible with the pieces we have plus some tweaking up front (and a real top pairing on the back end). In fact, I think it's probably the ideal for us given what we have already - a lot of skilled players. Sure, we need to change the makeup, but attempting to totally revamp things is just making more work rather than playing to one of the few strengths our lineup has.
And as for the response I'm expecting to get of "well if they're so good at scoring, why don't we score more?", I just will go back to the defence. You're never going to get much chance to score if your dmen can never get you the puck on the fly. We need to get a real top-pairing puckmover desperately and I'm of course comfortable with trading our forwards for one. But there's no point refusing to play/build 3 scoring lines before that trade happens. Concentrating our skill on one or two lines just makes us easier to shut down. I'd say McLellan agrees too, based on how he's been shuffling lines around. There's always a 'scorer'/skill player on each of the top 3 lines.