Not necessarily. Because the underlying rendering engine of both Safari and Chrome are open source, there exists a pool of software developers outside the company that are familiar with code. This means that there are people that these companies can hire who would be productive from day one. You cannot say this about Microsoft. How many people are familiar with the inner workings of trident outside of Microsoft?
What most web developers are more familiar with are the myriad ways to get around the inner workings of Trident, so that their websites can work from a more-or-less even playing field.