Hi,
The margin on a top-of-rack switch is very low. 48 port gige with 10GE uplinks are basically commodity boxes, with plenty of competition. Saving $100 on the bill of materials by cutting out some buffer makes the box more competitive when it's at a $2k price point.
The list of 10GE TOR switches I sent earlier are list from $20K to $100K So actual purchase cost for us would be $10K to $30K $500 for some (S)(Q)(bla)RAM shouldn't hold back a vendor from releasing a bitchin switch.... Again this argument does not explain why there are 1GE aggregation switches with deep buffers..
Also, as was pointed out to me privately, it is also important to loook at adaptive queue management features. The most famous is WRED, but there are other choices. Having a queue management solution on your routers and switches that works in concert with the congestion control mechanism used by the end stations always results in better goodput. Many of the low end switches have limited or no AQM choices, while the higher end switches with fancier ASICs can default to something like WRED. Be sure it is the deeper buffers that are making the difference, and not simply some queue management.
All true... Still no reason why not to offer a deep buffer TOR...