Let me re-iterate that OpenSprinkler uses a 8-bit microcontroller with a classic Microchip Ethernet controller that doesn’t have hardware TCP/IP stack. Instead, it uses software defined TCP/IP stack. The other devices on your network you are referring to are probably all based on 32-bit microprocessors running some sort of Linux variants. It’s really unfair to compare OpenSprinkler with these other devices.
And if you ask why OpenSprinkler is based on such underpowered hardware: it’s because it started as an open-source DIY kit, which users can buy and solder every single component to build their own OpenSprinkler. Today it’s still the only open-source sprinkler controller on the market. Look around and if there is another open-source sprinkler controller (which means both the hardware schematic and software are publicly available), let me know. The DIY kit restricted the number of options for choosing chips: only through-hole chips can be selected, and Microchip’s ENC28J60 is the only Ethernet controller that has a through-hole package. If it didn’t start as a DIY kit, I would have chosen a completely different set of components.
The Ethernet is based on the open-source EtherCard library. It’s not perfect, but it works reasonably well. I’ve personally done a lot of ping tests myself, and I’ve never seen the kind of ‘down’ times as you described. So I suspect the issue may be specific to your particular unit, and maybe to your particular network setup. Also, not understanding how these heartbeat and Homeseer apps work does not really help me figure out the cause: perhaps when a ping fails, they continuously send multiple pings trying to get an answer, and these multiple pings will only make the situation worse by saturating the controller.
In the end, if you feel OpenSprinkler is not for you, simply return it and we are happy to issue a full refund. As much as I want it to be, I have to be honest and admit that the product is not a perfect solution for everyone.