This can be quoted from Kapeselus, a blizzard employee on the EU beta forums:
Show nested quote +
You copied the first sentence, while the rest of the paragraph answers your question for the most part. StarCraft was made in the 28k-56k modem era and because the game is not that demanding, today (many years later) it is possible to play against American and (some) Korean players (still not Chinese for example, because of latency). Even in Warcraft III if you wanted to play against someone from the USA being in Europe it would mean ~250ms and possibly some spikes. In case of players from Asia or Australia for that matter it would be much higher and rarely stable. How many times have you played on the Lordaeron (US) or Kalimdor (Asia) gateway in e.g. WC3 or any newer games than BW for that matter? What was the percentage of players you could play against without lag issues? Would you like to jump from game to game constantly and leave, discouraged by huge latency? Also think about your opponents - wouldn't it affect them as well? I personally just cannot see players not getting frustrated by lags given how many discussions we have had that 125ms in-built latency is way too high. I don't even mention the matchmaking, because it would be unplayable and with proper filters it would match you against European players only anyway.
Please reconsider and don't rage without thinking it over. I am sure it will be possible in the future, but for now “the technology's just not there yet”.
I don't understand how "the technology's just not there yet" when throughout beta people have been playing on the EU server from US/Asia and vice versa. Look at the HDH tournament for example, the biggest SC2 tournament to date. Players such as Idra, WhiteRa, ret, and TLO played their tournament matches on the US beta server from overseas in Korea and Europe. Yes, there would have been higher latency than normal, but there were minimal lag issues and the tournament was a huge success.
That being said, I really respect the fact blizzard is attempting to minimize lag issues in order to improve the playing experience as much as possible. A 125ms buffer feels much better than a 250ms one, and nobody likes playing with laggers. The problem is, without cross-realm, you will have people account sharing and buying additional copies to bypass this restriction anyways. It will be reduced, but certainly not prevented.
Alot of casual players will deal with the fact that they cannot play cross-realm, and as a result the gameplay experience will improve with regards to latency (though lots of casuals also have friends overseas).
Blizzards current policy on cross-realm play hurts the competitive scene the most. You will see account sharing and people purchasing additional copies of the game just so they can bypass this restriction. Not only does it hurt the pockets of your most loyal fans, but it makes competition on a global level difficult. If blizzard truly wants to make SC2 an esport, some sort of cross-realm functionality, if not just for tournaments, really needs to be there.
Suggestion: Allow cross-realm, but make sure the auto-matchmaking system for both ladder and UMS match based on latency/region. I understand this would be a large undertaking and probably will not happen, but I see it as the best possible solution balancing gameplay quality and including cross-realm. It would allow people to play with friends and competitors overseas in private custom games, but maintain a low-latency experience elsewhere.
Edit: Better yet, just disable matchmaking for players who come from IP address ranges from other realms (or disable it if your latency is above Xms). (I.e. if you are from Korea and you log on to US it will say something along the lines of "Matchmaking in this region is disabled for your account, please use suggested realm"). This would allow them to play tournament games and play with friends (in private customs), preserve game quality, AND it would require less implementation than matchmaking based on region/latency.
Example w/ suggested functionality:
Korean player on EU server wants to queue for a match. He will only be matched with people of similar high latency or region. The gameplay experience is preserved.
The same player wants to take part in a tournament being hosted on the US server. He can do so in private custom games, and the tournament organizers can decide at their own discretion at which point high latency becomes unacceptable.
The same example without suggested functionality:
Korean player on EU server wants to queue for a match. He will either share accounts, purchase an additional copy, or be discouraged to compete with players overseas. The gameplay experience is not preserved. This also gives the public appearance that this policy may be a money grab.
The same player wants to take part in a tournament being hosted on the US server, he will account share or shell out 60 bucks, bypassing the realm restriction.