OV
I see two key reasons why ITV (and C4 for that matter) don't offer HD or higher quality SD streams currently.
The first as already pointed out is down to ITV2-4 HD being subscription services, and as such they don't want to provide the HD programming from those channels for free online.
The second will be the bandwidth required for HD and higher quality SD. HD and higher quality SD of course require the videos to be encoded at a higher bitrate (significantly so for HD), which in turn requires significantly increased bandwidth to deliver those streams. Increasing the bandwidth required no doubt requires forking out much more money to their content delivery network partners, and as we all know commercial broadcasters like to keep their costs low to increase their profit or what they can invest in programming. The BBC doesn't have this issue, and therefore does have HD streams, as they have guarranteed revenue to cover the costs of running iPlayer in the form of the portion of the TV license allocated for online services. This is also why Sky subscribers do have HD streams, as Sky host themselves streams delivered to their customers, and therefore take on the bandwidth cost for the broadcasters as a way of enhancing their HD proposition and increasing HD subscribers.
The first as already pointed out is down to ITV2-4 HD being subscription services, and as such they don't want to provide the HD programming from those channels for free online.
The second will be the bandwidth required for HD and higher quality SD. HD and higher quality SD of course require the videos to be encoded at a higher bitrate (significantly so for HD), which in turn requires significantly increased bandwidth to deliver those streams. Increasing the bandwidth required no doubt requires forking out much more money to their content delivery network partners, and as we all know commercial broadcasters like to keep their costs low to increase their profit or what they can invest in programming. The BBC doesn't have this issue, and therefore does have HD streams, as they have guarranteed revenue to cover the costs of running iPlayer in the form of the portion of the TV license allocated for online services. This is also why Sky subscribers do have HD streams, as Sky host themselves streams delivered to their customers, and therefore take on the bandwidth cost for the broadcasters as a way of enhancing their HD proposition and increasing HD subscribers.