|For sports 60 frames per second is better than 60 fields per second, thus 720p60 is better than 1080i. (My opinion. Also the opinion of ESPN.) Given constrained bandwidth, 720p can be lower in artifacts than 1080i. Interlaced video is just harder to compress.
1080i is a good choice for HBO. Most of their content is movies at 24 frames per second. Mapping this to 60 fields or 60 frames is roughly the same. The 24 fps screws up motion a lot. The choice of i or p isn't going to make much difference.
De-interlacing well is hard. Many TVs have good de-interlacers. Some don't, which impacts the quality of interlaced video.
Another reason I'm skeptical about 4k in the home is that 1080p60 hasn't caught on. It's not very hard in 2012. Just lots of little problems that could be addressed easily if there was enough motivation.