Yes in some cases the default is quite expensive – the same was there with SQL Azure (though they have changed that recently) and it had created a good amount of bill for us (though for their credit, Azure did refund in all such occasions because we didn't use the capacity at all).
However, I don't know why the alert system doesn't have an option to say "here's my budget, alert me as soon as when my daily pace is set to exceed the monthly budget" instead, you have % of budget amount consumed based alerts, like you can get email if you say 50% of my budget is consumed, which happens every month so kinds of defeat the purpose of an alert.
We ended up creating a simple solution (cloudalarm.in – in beta) that provides such budgeted pace based alert and more ways to get instant alert which isn't possible with usage based alerts.
We ended up creating a simple solution (cloudalarm.in – in beta) that provides such budgeted pace based alert and more ways to get instant alert which isn't possible with usage based alerts.