Irony.
5e has both a Basic type line (Basic, Starter, and Essentials) as well as the normal line.
It essentially (hahaha...okay...maybe you don't see my pun there) has two lines going.
It's more pronounced in 5e than any other edition previously since WotC took over.
3.X had it with their Basic D&D, but that only went up to level 3.
Basic D&D in 5e goes up to level 20 for 4 classes if one wants to stick to Basic. The Starter box goes up to level 5 and the Essentials box goes up to level 6.
I'd say a HUGE reason for 5e's success is actually DUE to having two lines.
It follows the same reason why TSR D&D had 25 million players...it is BECAUSE of these two lines that it meets it's success.
When they dropped the two lines TSR D&D ran into massive trouble (yes, I know other reasons are listed for it's failure...but there is that thing where sales dropped off after BECMI/RC was dropped by some anecdotes).
Two Lines following the Basic/Advanced idea I think are essential for a greater amount of success.
It also is essential that they are largely compatible (sure, some can point out many differences between B/X, BECMI, and AD&D, but let's face it, they are mostly compatible and there are a TON of players that went from the B/X and BECMI to AD&D).
This is one of the core items I consider why 5e is successful and why I support the idea for an Essentials Kit building off the Starter box and a Basic ruleset online.
It introduces new players to the game without that sense of overload. It makes it so that they can have their alternative if they like it (basic pdf). It ALSO means that they now are familiar with the rules and I feel MANY who start on this path eventually start playing the full 5e game. Just like B/X and BECMI got a TON of gamers playing AD&D, I feel the Basic line of 5e does the same thing.
There IS a split of the line with 5e between Basic rules and the full rules, but I think it BENEFITS 5e and has brought in FAR MORE gamers to 5e and buying 5e books than any detrimental effects people think two lines bring (just like BECMI did for AD&D).
The current Basic line (Starter Box, Essentials Kit, Basic Rules) actually has MORE core rule supplements than Holmes (1) or B/X (2) did. It has less than BECMI (5) did, but I think that the OPTIONS available for various race and class combos actually make it so that there are MORE options of playable classes in the core rule sets (but only if you include the Basic PDF probably, though essentials comes close if not more overall as well).
So, I think there actually ARE two different lines of 5e right now, but just like B/X and BECMI complimented AD&D and made the brand stronger, the split actually makes 5e stronger and sell better as well.
PS: Just ask most BECMI players as well as B/X players. I bet you'll find that almost all of them (though I admit, there are a few holdouts) also played AD&D. The same eventually goes for those who play the Starter Box, Essentials Kit, or the Basic PDF...eventually I feel those that stick with the game also go one to buy at least some of the core rule books and some of the supplemental rulebooks.