The gaming industry has come a long way since the days when a pressed disc was the last word on a game's quality. Studios needed to be meticulous during production to catch every little bug and make sure their titles were as polished as possible, as even one game-breaking glitch which slipped through the cracks would be beyond repair if it was discovered once in the hands of players.
Consequently, the move towards releases that can constantly be updated, changed, and tweaked thanks to the power of the internet has been a bit of a double-edged sword. It's meant that developers have the ability to fix mistakes they may have missed, but also leads to a pervasive mentality of shipping games to hit rigid release dates regardless of their quality, in the confidence that the problems can be solved at a later date.
In some cases though, titles have benefited immensely from the ability to constantly be worked on. Fan feedback is an invaluable commodity, and being able to take a step back, analyse what works and what doesn't and adjust accordingly has led to some games that were disasters at launch turning into pretty perfect releases after a few months of additional dev time.