You're missing the point: in many cases, choice of C is not ideological but practical. I love Modula-3 and OCaml (and ML's incorporation of Modula's module system in general); yet I'm using C++ for the project I am working on. From even the purely technical point of view, despite all the features OCaml has that I enjoy, building this system wouldn't be feasible -- I need shared memory concurrency and multi-core support, for example.

On the other hand, memory leaks occur just well in memory-safe languages (looking at Modula-3, I see a WeakPtr type -- which is there for this very reason). Finally there are also many reasons to want to have manual control over memory -- which when using high-level languages, ends up looking very much like C programming (e.g., Unsafe module in Java). However, you're essentially on your own when doing this.

By the way, memory debuggers are just one example -- plain debuggers are another, tools for tracing the code execution, performance tuning, etc... are another. As are mature and universally available libraries.

I don't mean to disparage high-level languages: I greatly enjoy programming in them and would like them to expand. Yet we're talking about existing code -- and in this case, C's maturity and universality (as a "lingua franca" of programming) are unrivaled. Nothing stops one from using -- and enjoying -- both advanced high level languages and C.