This is certainly the dominant perception coming out of SV these days. But since the vast majority of startups fail and have no more time (or rather, will) to collect development metrics than they do to implement TDD, I doubt we'll ever have any kind of real validation of this perception.

I suspect it comes from a combination of a) young coders more likely to find themselves at a startup, who are also more likely not to have developed TDD habits and 2) VCs, angels and the like who, while well-intentioned, likely push this notion that TDD is for "mature" companies and/or, "we'll pay that off later, just get the code out the door." Young CEOs, CTOs, founders and the like who need to validate all of their startups' initiatives and practices probably are swimming upstream if they want to go TDD from the ground up.

For some instances of prototyping and lightweight apps (like Obie mentioned), this is probably fine. In my experience though, the short term effects of playing "shipping" against "craft/testing" settle in within a matter of days and weeks, not months and years, and the mid-term effects of technical debt when a startup moves into "mature" phase (again, a much shorter time span than anyone realizes) are such that the idea of "debt" and "what are we going to do about it" becomes a/the dominant conversation on the team. I've experienced both sides.

My perspective: the cost of TDD is mainly to young coders who need to learn it and find the curve daunting. Teams built around these type of otherwise talented devs really would incur significant up-front cost to booting up a CI/Test server and getting past the curve to the point where the team is moving at a comfortable pace, comparable to where they were before implementing TDD. In this case, TDD is a very hard sell. I don't know how to solve that problem, other than changing the SV/startup culture to the point where those holding the purse strings see the benefits of craft/testing as being as attainable in the mid-to-short term as they are in the long term (and in my experience, they absolutely are).

If you have buy-in to TDD/craft (I can't really separate the two in my mind) from the top-down, and you have experienced coders that can facilitate implementing, in my opinion it's absolutely worth pursuing. The second-order effects of a culture built on these principles kick in with a vengeance right when a startup needs it: at crucial pivot points.

When you have to change your business assumptions quickly -- and this usually happens weeks or months into the starup lifecycle -- would you rather do it on a codebase where, say, your authentication/authorization and user model was tightly coupled to other concerns or not? Would you rather know with a relative degree of confidence that the changes you're making are not breaking core concerns? Wouldn't you rather do this quickly, rather than thrash around in unclear code that you'd rather just rewrite (you know, like it felt when we started!)?

And if you're pivoting, are you not more likely to be less cash-rich, under more pressure and in need of some really good success right now, since pivoting probably implies that former assumptions did not pan out the way you'd hoped? Isn't that exactly the point where you'd like to both reuse the code you need and know that things are still working around your baseline assumptions that seemed so clear a few short weeks/months ago?

I would think at this point the benefits to a startup in this mode, of a clean, fast-moving and validated codebase, of the kind that good TDD tends to produce, should be patently freaking obvious. Just my opinion.