"Do I need a gaming keyboard?"
In essence, no.
You can operate on a standard computer keyboard reasonably well for gaming. However, if you were to ask "Will a gaming keyboard improve my overall computing gaming experience?" then I would have to answer, yes, considerably so.
Below is a tongue in cheek list of the potential in-game advantages that a gaming keyboard offers when compared to that of a standard regular keyboard. It is also worth noting that each specific model of keyboard (both gaming and non-gaming) will have its very own unique set of advantages and disadvantages, so some aspects of a particular keyboard may hold over some keyboards but not others.
High-Speed Key Input
One of the most attractive features of gaming keyboards is there incredibly high report rates, where the Razer Blackwidow Ultimate boasts a speed of (1000Hz) 1 millisecond response time, executing actions and commands pretty much immediately. They also assure you with the confidence that multiple complex key combinations will actually work and won't be interrupted and ignored. This allows you to gain those vital few milliseconds 'in game' that could literally mean the difference between life and death.
Gaming Key Infrastructures
You will find with most gaming keyboards a high amount of detail has gone into even the very feel of hitting a key. A range of options are available such as the dome-switch to the hall-effect keyboards, all giving the user a different feel to hitting a key. However, a popular key structure amongst gamers is the 'mechanical key infrastructure' which means in some various form -- they use physical switches below all the key buttons within the keyboard. Although, it doesn't sound too flattering -- when such technology is modified and applied to a keyboard such as the Razer Blackwidow Ultimate it allows you to actuate commands a lot quicker and more efficiently than that of your standard keyboard (and in this case more so than most other gaming keyboards as well), as not as much pressure (and effort) is needed to be applied in order to carry out the action on screen -- and with this particular model a crisp and 'distinctive tactile kickback'. The idea is that it allows you to save time in order to give you a distinctive gaming edge, as well as giving you a greater feel and sense of gaming from the keyboard. However, when it comes to key infrastructures it is all down to preferences, some will work for you, some simply won't -- so I recommend that you try out a range of key infrastructures and see which you get a better feel for.
LCD Gaming Panel
A really great feature about certain gaming keyboards such as the Logitech Gaming Keyboard G510 is the 'instant intel' provided through the on-board gaming panel, where "vital in game stats, system performance, VOIP communication data" can be accessed without the need for quitting or differing the game in hand. Hence, not only saving you time from having to pause and find the stats, but also adding to a greater 'in-game' excitement.
Other specific models offer their very own unique advantages (and if you know of any please share some of them below and their corresponding model) such as the numerous programmable G-keys, for a greater variety of commands offered by the Logitech G510. The wonderfully sculpted Kinesis KB500 which offers a high tech ergonomic option for those who view comfort and control as a high priority. As well as the more modern range, of the one handed gaming keypad such as the Razer Nostromo (which I have to say I am particularly fond of). There are a whole range of features that come with specific keyboards, so if you are thinking of buying one be sure to conduct a fair amount of research to something that you think can satisfy your needs.
So to answer your question again 'Do I Need a Gaming keyboard?', essentially no, but from the options above -- not only can you improve your gaming performance with a gaming keyboard but you can also improve your overall gaming 'experience'. I personally find that I get in the mood for gaming by even just looking at my friend's Razer Blackwidow Ultimate. This being said, you may not find that a 'gaming keyboard' doesn't really add anything to your gaming style or experience at all and that you are just as happy with a regular keyboard, it is all down to preferences. But, if you haven't tested out a decent gaming keyboard (such as the Blackwidow) yet, then I definitely advise to give it at least a try, I am pretty sure you will see a distinct positive difference.