Jessie, according to JamesH, and he should know, software decoding of MPEG2 isn't likely to be possible on the RPi without the GPU routines enabled.
I understand why it wasn't included, the license cost was too high, but it's like being sold a car with air-con when you haven't got a license to wind the windows down. All the windows can wind down but there a padlock on each handle and you're not allowed to buy a key.
If I wanted to use the RPi with a DVB-T USB dongle to record and/or view any live terrestrial TV from the BBC (Other freeview channels are available, but all MPEG-2.) I can't decode on the RPi itself. There's no point having it stream the recordings to a big power hungry machine to transcode and get sent back to the RPi. I can transcode all my old recordings but to watch live TV I'll still need another option.
Having to run another machine to transcode MPEG-2 to h.264 would cost more in electricity each year than the £2.50 MPEG2 license would forever. It's just a shame that the hardware can do it easily, but we can't pay an additional fee to enable it.
The result of this is that to get MPEG-2 decoding on the Pi I'd need to build an add-on, with hardware MPEG transcoder chip (almost certainly ARM based), and stream the TV feed to that, back to the Pi and to the GPU as MPEG-4, and on to the TV. Buying another chip with the same decoding capability as the Pi's GPU but with the MPEG-LA fees paid with the chip purchase price.
As an aside, I think you'll find you should actually be directly paying MPEG-LA a licensing fee as you use Handbrake to transcode MPEG-2 to MPEG-4. Have you done? If not you could face (unlikely) court action from the patent holders.
Anyway, I understand that different people will be frustrated by different limitations of the design and the minimal number of compromises that had to be made in order to hit the incredible price point that the foundation did is nothing short of mind boggling.
Robot builders may wonder why only one camera interface was connected when they want stereo vision (PCB routing nightmares, no doubt), people building portable units may have preferred an LVDS interface for lcd screens. Those decisions have been made and can't be changed, but the frustrations felt by those wanting hardware accelerated decoding of MPEG-2 is different, the RPi can do it, the chip is capable, we're just locked out.